San Francisco star defensive end Nick Bosa tore the ACL in his right knee and will miss the rest of the season

San Francisco 49ers defensive end Nick Bosa walks off the field during the first half of an NFL football game against the Arizona Cardinals, Sunday, Sept. 21, 2025, in Santa Clara, Calif. (AP Photo/Godofredo A. Vásquez)

SANTA CLARA, Calif. (AP) — San Francisco star defensive end Nick Bosa tore the ACL in his right knee and will miss the rest of the season, according to a person familiar with the situation.

Bosa hurt his knee in the first half of a win over the Arizona Cardinals on Sunday and didn't return to the game. Bosa gave a thumbs-down to someone in the crowd after the injury, but initial tests did not show a torn ACL.

Coach Kyle Shanahan said after the game that more tests would be needed to determine the severity of the injury. The person familiar with the situation told The Associated Press on Monday that those tests showed that Bosa had torn his ACL and his season was done. The person spoke to the AP on condition of anonymity because the team hadn't made an announcement.

ESPN first reported the extent of the injury.

This is the second time Bosa has gone down with a season-ending ACL tear early in the season. Bosa tore the ACL in his left knee in Week 2 of the 2020 season and missed the rest of that season.

That marked the only time in Bosa's first six seasons in the NFL that he didn't record at least nine sacks in a season; he's been one of the most productive edge rushers ever since being drafted second overall in 2019.

Bosa has made the Pro Bowl in all five of his healthy seasons and won the AP NFL Defensive Player of the Year award in 2022, when he lead the league with 18 1/2 sacks.

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San Francisco 49ers' Nick Bosa (97) tries to stop Arizona Cardinals' James Connor in the first quarter of an NFL football game in Santa Clara, Calif., Sunday, Sept. 21, 2025. (Scott Strazzante/San Francisco Chronicle via AP)

Bosa's 74 1/2 sacks in the regular season and playoffs are the fourth most in the NFL since he entered the league in 2019, and his 280 total pressures are the most in the NFL in that span, according to Sportradar.

The injury to Bosa is a significant blow to San Francisco's young but promising defense. The Niners had been relying on Bosa to solidify the defensive line that is counting on rookies Mykel Williams, Alfred Collins and C.J. West to make contributions.

With Bosa out, San Francisco's top options at defensive line are Williams, who has been playing both inside and outside so far this season, and veterans Bryce Huff and Yetur Gross-Matos.

“I feel like it was the whole group, like the whole D-line room said we’ve got to step it up because Bosa is a great player for us and he holds a heavy load,” Williams said after the game on Sunday. "So when we lose him, everybody has got to raise their game.”

San Francisco has overcome injuries to several stars to get off to a 3-0 start this season. Tight end George Kittle is on injured reserve after injuring his hamstring in Week 1, quarterback Brock Purdy missed the last two games with a toe injury, receiver Jauan Jennings missed Sunday's game with a shoulder and ankle injury and receiver Brandon Aiyuk is on the physically unable to perform list as he recovers from surgery after tearing his ACL last October.

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