San Francisco 49ers star defensive end Nick Bosa is expected to miss multiple games after suffering a calf injury during practice ahead of the team’s Week 3 game against the Arizona Cardinals.
Bosa pulled his calf during Thursday’s practice and is expected to be sidelined for “a few weeks,” according to ESPN. He has already been ruled out against Arizona, and the 49ers are determining whether the injury is serious enough to place him on injured reserve. [ESPN] [NFL]
The injury is particularly significant because Bosa had just returned from the torn ACL that ended his 2025 season. It also adds another problem to an already depleted San Francisco defensive line and removes the 49ers’ most accomplished pass rusher from a defense that had helped the team begin the 2026 season 2-0.
How Did Nick Bosa Injure His Calf?
Bosa was injured during practice on Thursday, September 24.
He had not practiced Wednesday, but that absence was initially described as a scheduled veteran rest day. Bosa has been receiving additional maintenance as he works his way back from the right ACL tear that ended his 2025 season. [San Francisco Chronicle]
The situation changed Thursday. Bosa did not return to practice and the 49ers added a calf injury to his designation.
Subsequent reports revealed that Bosa had pulled the calf during practice and would miss multiple weeks rather than simply being held out as a precaution. [ESPN]
How Serious Is Nick Bosa’s Calf Injury?
The 49ers have not announced a specific grade for Bosa’s calf injury, but the expected absence of several weeks indicates this is more than minor soreness.
ESPN’s Adam Schefter reported that Bosa “pulled his calf” and is expected to miss a few weeks. NFL Network’s Ian Rapoport similarly reported that Bosa will be out multiple weeks. [ESPN] [NFL]
That wording is important because the team has not announced a season-ending injury or a specific structural diagnosis.
The immediate question is instead whether Bosa can return within several weeks or whether San Francisco determines that putting him on injured reserve makes more sense.
Will Nick Bosa Play Against The Cardinals?
No.
Bosa will miss San Francisco’s September 27 game against the Arizona Cardinals. The 49ers ruled him out after determining that the calf injury would require a multi-week recovery. [NFL]
The injury removes the 49ers’ best individual pass rusher from an NFC West game as San Francisco attempts to improve on its 2-0 start.
When Will Nick Bosa Return?
There is no exact return date yet.
The current expectation is that Bosa will miss at least a few weeks. That makes an October return possible, but the 49ers have not identified a particular game as his target. [ESPN]
Calf injuries can also be difficult for edge rushers because the position requires explosive acceleration, sudden changes of direction and the ability to generate force through the lower body while battling offensive tackles.
For Bosa, San Francisco also has an additional reason to be conservative: he is only two games into his return from major knee surgery.
Could Nick Bosa Go On Injured Reserve?
Yes. The 49ers are considering whether to place Bosa on injured reserve. [ESPN]
Under NFL rules, a player placed on injured reserve during the regular season must miss at least four games before he is eligible to return.
That creates a roster-management decision for San Francisco.
If the team believes Bosa could return before four games have passed, keeping him on the active roster preserves the possibility of an earlier return. If doctors expect the recovery to take four games or longer, injured reserve would allow the 49ers to use his roster spot on another player.
The decision is complicated by the number of other injured players already on San Francisco’s roster and the NFL’s limit on how many players can be designated to return from injured reserve during a season.
Why Is Bosa’s Injury Especially Concerning After His Torn ACL?
Bosa suffered a torn ACL in his right knee during San Francisco’s Week 3 victory over Arizona in September 2025.
It ended his season and sent him through another lengthy rehabilitation. Bosa has now suffered three ACL tears during his football career, including major knee injuries in high school and during his second NFL season. [49ers]
He spent the 2026 offseason working back from the most recent tear and was ready for San Francisco’s regular-season opener.
The calf injury is a separate injury. There has been no report that Bosa reinjured his ACL.
But any lower-body injury so soon after an ACL rehabilitation creates an additional workload-management issue for the 49ers. San Francisco had already been giving Bosa scheduled rest as he rebuilt his normal football workload.
How Was Nick Bosa Playing Before The Injury?
Bosa had made an encouraging return through San Francisco’s first two games.
He did not record a sack against Miami in Week 2, but he generated four quarterback pressures and helped create sacks for teammates as the 49ers beat the Dolphins 35-13. [Niners Nation]
Bosa said after the game that he felt fully healthy following the ACL rehabilitation. [San Francisco Chronicle]
His impact also goes beyond sacks. Offensive lines frequently devote additional protection toward Bosa, which can create one-on-one opportunities for San Francisco’s other defensive linemen.
Why Is Nick Bosa So Important To The 49ers Defense?
Bosa is the centerpiece of San Francisco’s defensive front.
The 49ers selected him No. 2 overall in the 2019 NFL Draft, and he quickly developed into one of the league’s premier edge rushers. He won NFL Defensive Rookie of the Year in 2019 and NFL Defensive Player of the Year in 2022.
Bosa has also been selected to five Pro Bowls. [49ers]
His primary job is pressuring quarterbacks from the edge, but his presence changes how opponents construct their protection schemes.
An offense facing Bosa may use a tight end or running back to help an offensive tackle, slide protection toward his side or call quicker passes designed to get the ball out before Bosa reaches the quarterback.
Without him, offensive coordinators have considerably more freedom to devote blockers elsewhere.
Who Replaces Nick Bosa?
Rookie Romello Height is listed directly behind Bosa at right defensive end on San Francisco’s depth chart. [49ers]
Height has already flashed as a pass rusher. He recorded a sack against Miami in Week 2 and had been part of the defensive-line rotation before Bosa’s injury. [San Francisco Chronicle]
There is a complication, however: Height has also been dealing with a hand injury.
The 49ers can additionally turn to Ogbo Okoronkwo and Khalid Kareem for more edge-rushing snaps. Keion White starts at the opposite defensive-end position. [49ers]
Rather than expecting one player to reproduce Bosa’s production, defensive coordinator Raheem Morris will probably have to distribute his snaps among several players and manufacture additional pressure schematically.
Why Is The Timing So Bad For The 49ers Defensive Line?
Bosa’s injury is not occurring in isolation.
San Francisco was already dealing with significant injuries along its defensive front.
Defensive tackle James Thompson Jr. suffered a high ankle sprain against Miami and is expected to miss multiple weeks. Alfred Collins has also been lost to a season-ending injury, while Sam Okuayinonu is on injured reserve with a foot injury. [San Francisco Chronicle]
Mykel Williams, another potential edge-rushing option, has also been unavailable while recovering from an ACL injury.
That means the 49ers are not simply removing Bosa from a completely healthy defensive-line rotation. They are losing their best pass rusher while several of the players who could normally help absorb the loss are also unavailable or injured.
Could The 49ers Sign Another Pass Rusher?
That possibility becomes more relevant with Bosa expected to miss multiple weeks.
Even before Bosa’s injury, the 49ers had been exploring defensive-line help. San Francisco had reportedly been in contact with veteran edge rusher Leonard Floyd and other available players after injuries reduced its depth. [Niners Nation]
Bosa’s absence gives the front office another reason to consider adding a veteran.
Any signing would not necessarily be expected to replace Bosa’s production. The more realistic goal would be adding enough experienced depth to keep San Francisco’s existing defensive linemen from being overloaded while Bosa recovers.
How Could The 49ers Defense Change Without Bosa?
The biggest change could be how San Francisco creates pressure.
When Bosa is healthy, the 49ers can often generate pressure with four defensive linemen. That allows the remaining seven defenders to concentrate on coverage.
Without an elite edge rusher consistently threatening the quarterback, Morris may have to become more creative.
That could mean:
- more blitzes from linebackers and defensive backs;
- more defensive-line stunts and twists;
- moving pass rushers around before the snap;
- using larger rotations to keep the defensive line fresh;
- asking Keion White and the other edge defenders to take more one-on-one pass-rushing snaps.
San Francisco has already shown some ability to create pressure from multiple players. Against Miami, Bosa’s four pressures helped teammates finish plays even though he did not personally record a sack. [Niners Nation]
How Does Bosa’s Injury Affect The Secondary?
The effects can extend well beyond the defensive line.
A strong four-man pass rush reduces the amount of time defensive backs have to cover receivers. If Bosa forces a quarterback to throw early, cornerbacks and safeties do not have to maintain coverage as long.
If the 49ers need to blitz more frequently to replace Bosa’s pressure, they may also have fewer defenders available in coverage.
That could put additional responsibility on cornerbacks Renardo Green and Deommodore Lenoir and safeties Malik Mustapha, Ji’Ayir Brown and Marques Sigle.
San Francisco’s secondary has started the season well, giving Morris some flexibility while he figures out how to compensate for Bosa’s absence.
What Does The Injury Mean Against Kyler Murray And Arizona?
Bosa’s first missed game comes against a quarterback whose mobility makes edge discipline particularly important.
Arizona quarterback Kyler Murray can extend plays outside the pocket and punish defenses with his legs. Edge defenders therefore have to balance attacking the quarterback with preventing him from escaping around the outside.
That makes replacing Bosa more complicated than simply generating sacks.
San Francisco’s replacement edge defenders will need to maintain rush-lane discipline while trying to pressure Murray in Sunday’s NFC West matchup.
How Does Nick Bosa’s Injury Affect The 49ers’ Season?
The immediate effect is significant but not necessarily catastrophic if the current “few weeks” timetable proves accurate.
San Francisco has started 2-0, beating the Los Angeles Rams in Week 1 and Miami 35-13 in Week 2. The offense has played efficiently, while the defense has shown it can generate pressure from players other than Bosa.
But losing Bosa removes the player opponents are most likely to design their blocking plan around.
The larger concern is accumulation. San Francisco is already dealing with injuries at wide receiver and along the defensive line, making Bosa’s absence another test of a roster that has been forced to use its depth almost immediately.
Could Bosa’s Injury Have Playoff Implications?
That depends primarily on how long he is out.
If Bosa misses only a handful of games and returns healthy, San Francisco could absorb the absence without it becoming a defining event in the season.
If the calf problem lingers, however, the consequences become much larger. Pass rush is one of the most valuable components of a playoff defense, and the 49ers constructed their defensive front around Bosa’s ability to disrupt quarterbacks without requiring constant blitzing.
The team’s decision on injured reserve should provide an early clue. Keeping Bosa on the active roster would preserve the possibility of returning before four games have passed. Moving him to IR would guarantee a longer absence.
What Is Nick Bosa’s Injury History?
Bosa’s injury history makes any lower-body problem noteworthy.
He tore an ACL during high school and then tore the ACL in his left knee during the 2020 NFL season. He returned from that injury and eventually became the NFL’s Defensive Player of the Year.
He then tore the ACL in his right knee during Week 3 of the 2025 season against Arizona. Bosa described the early portion of that rehabilitation as difficult before working his way back in time for the 2026 season. [49ers]
The new calf injury is not reported to be another ACL injury, but it interrupts his comeback only two games into the season.
What Is The Latest Nick Bosa Injury Update?
As of September 25, the situation can be summarized this way:
- Bosa pulled his calf during Thursday’s practice.
- He will not play against the Arizona Cardinals in Week 3.
- He is expected to miss multiple weeks.
- The 49ers have not announced an exact return date.
- The team is considering whether to place him on injured reserve.
- The injury is separate from the torn right ACL that ended his 2025 season.
- Romello Height is Bosa’s listed backup, with Ogbo Okoronkwo and Khalid Kareem among the other potential edge options.
- San Francisco was already dealing with multiple injuries along its defensive line.
The most encouraging part of the initial report is that Bosa is expected to miss weeks rather than the remainder of the season. The biggest concern for San Francisco is that the injury interrupts his comeback from ACL surgery just as he was beginning to look comfortable again.
For a 49ers defense built around generating pressure from its front four, there is no simple replacement for Bosa. Until he returns, San Francisco will have to compensate with depth, rotation and scheme rather than expecting one player to reproduce what its five-time Pro Bowl edge rusher provides.
