Devastating Blow: Nick Bosa Out for Season After ACL Tear, 49ers Defense Faces Urgent Challenge Ahead
San Francisco 49ers defensive end Nick Bosa will miss the rest of the 2025 NFL season after tearing his ACL in Sunday’s 16-15 win over the Arizona Cardinals. Head coach Kyle Shanahan confirmed the news on Monday, following an MRI that revealed the full extent of the injury.
The injury happened late in the first quarter when Bosa, rushing Cardinals quarterback Kyler Murray, got tangled with offensive linemen Kelvin Beachum and Evan Brown. As Brown came in to assist, Bosa’s knee bent awkwardly, causing immediate concern.
After spending time in the medical tent, Bosa attempted to stretch and assess his leg but eventually walked to the locker room. Cameras caught him giving a thumbs-down gesture to family members in the stands—a moment that now feels all too telling.
“It didn’t look good,” Shanahan admitted after Sunday’s game. “We were hoping for better news, but unfortunately, the MRI confirmed our worst fears.”
Second ACL Tear for Bosa
This isn’t the first time Bosa has faced a serious knee injury. In 2020, he tore the ACL in his left knee during Week 2 against the Jets, forcing him to miss the rest of that season. He has also dealt with knee issues dating back to high school, including playing through a partially torn right ACL in 2015.
Despite these setbacks, Bosa has consistently bounced back stronger. In 2021, he returned to start all 17 games, recording 15.5 sacks and helping the 49ers reach the NFC Championship Game. He followed that with a dominant 2022 season, winning Defensive Player of the Year after leading the league with 18.5 sacks.
Now, at 27, Bosa faces his second ACL recovery. While modern medicine improves outcomes, having ACL tears in both knees creates new challenges for his long-term durability.
What This Means for the 49ers
Bosa’s injury is a huge blow for a 49ers defense already undergoing changes this season. Through the first two games, he had two sacks, eight quarterback pressures, and a strong 21.9% pass rush win rate. Losing his presence on the line leaves a significant gap in the team’s pass rush.
The 49ers will look to free agent Bryce Huff, rookie Mykel Williams, and other edge rushers like Yetur Gross-Matos to step up. Veteran left tackle Trent Williams, a close friend of Bosa, acknowledged the difficult road ahead.
“Replacing Nick isn’t realistic,” Williams said. “It’s going to take a collective effort from everyone on defense to fill the void. But we’ve got a good group, and I know they’ll step up when it counts.”
What’s Next for Bosa
Bosa will now shift his focus to surgery and rehabilitation, with hopes of returning at full strength for the 2026 season. Having rehabilitated an ACL tear before, he knows the process, but the cumulative toll of multiple knee injuries will inevitably raise questions about his longevity in the NFL.
The 49ers, meanwhile, will receive about $7 million in salary cap relief for 2026, thanks to an insurance policy tied to season-ending injuries, giving the team some flexibility to address roster needs.
As the 3-0 49ers work to maintain their strong start, they’ll face the challenge of competing without their best defensive player. For now, their Super Bowl hopes rest on the shoulders of a defense trying to fill the void left by one of the NFL’s premier pass rushers.
