49ers Lose Defensive Star Nick Bosa for the Season After His ACL Tear

The 2022 Defensive Player of the Year also tore his ACL in 2020, missing 14 games as San Francisco finished 6-10.

Nick Bosa of the San Francisco 49ers celebrates a sack against the Saints at Caesars Superdome in New Orleans on Sept. 14, 2025. Sean Gardner/Getty Images

After defeating the Arizona Cardinals, 16-15, on Sunday, the San Francisco 49ers moved to 3-0, making them one of a half-dozen undefeated teams. But their quests for 4-0, a playoff berth and a long-awaited sixth Super Bowl championship took massive hits on Monday.

The team revealed that defensive end Nick Bosa, the 2022 Defensive Player of the Year, suffered a torn ACL in his right knee in the victory. Bosa’s season is over after just three games, which marks the second time he’s suffered this injury before the calendar has even flipped to October. Back in 2020, Bosa tore his left ACL just two games into the season, thus missing the last 14 games.

This is actually the third ACL tear for Bosa, as he first partially tore the ligament in his right knee as a high school senior in 2015. The previous two times it occurred, he did manage to play in all of his team’s games the following season, but his 2025 NFL season is over just two games and one quarter into the campaign.

The latest injury occurred with about one minute left in the first quarter. Bosa, rushing from the offense’s left side, engaged with Cardinals left tackle Kelvin Beachum. Then left guard Evan Brown came over for a double team and knocked Bosa to the ground, buckling his knee awkwardly.

That was his last play of the game. He slowly walked to the sideline, was treated by trainers, and then entered the medical tent. After a couple of minutes, he emerged and began stretching and doing high-knees, as it appeared he had avoided serious injury. But he then headed to the locker room, and while walking there, Bosa gave a thumbs-down gesture to someone in the crowd. It was pretty evident he knew that his season was over.

Bosa ends his season with 17 tackles, three sacks, and two forced fumbles, including knocking the ball free during his 14 snaps in Week 3. He had sacks in each of the first two weeks and looked every bit like the player who won DPOY in 2022, instead of the player who had a down year in 2024. Last season, Bosa’s nine sacks were tied for his fewest in a season, outside of 2020.

He is under contract with the 49ers for three more seasons after signing an extension in 2023. That year, Bosa became the highest-paid defensive player in NFL history by signing a five-year, $170 million deal. He held that title until this month, when Micah Parsons signed a contract with the Green Bay Packers following his trade from the Dallas Cowboys, making Parsons the highest-paid defender, with Bosa’s deal now ranking second.

The 49ers replaced their entire starting defensive line from last season, save for Bosa, so now they will have a completely new unit with him going on injured reserve. None of the other three starting linemen has notched a sack this year, which shows the team’s reliance on Bosa. San Francisco would seemingly promote defensive end Bryce Huff to the starting lineup—and he does have two sacks as a reserve this year—but he’s started just 13 of a possible 69 games across his seven-year career.

Bosa, a five-time Pro Bowler who was also the 2019 Defensive Rookie of the Year, wasn’t the only household name to suffer a season-ending injury in San Francisco’s win over Arizona. James Conner, the starting running back for the Cardinals, who is a two-time Pro Bowler, suffered a gruesome foot injury in the game. On Monday, the Cardinals said Conner will need surgery and will miss the rest of the year.

The 49ers have had a string of injured stars, with three of their best offensive players sidelined.

Wide receiver Brandon Aiyuk has yet to play this year after tearing his ACL in Week 7 last season.

In Week 1 this year, the Niners lost both quarterback Brock Purdy and tight end George Kittle. Purdy has injuries to his toe and shoulder and is questionable for Week 4. Kittle suffered a hamstring injury, was placed on short-term injured reserve, and won’t be eligible until Week 6.

Even with all of these setbacks, the 49ers are 3-0 for the third time under ninth-year head coach Kyle Shanahan. The two previous times the Niners started 3-0 (2019, 2023), they advanced to the Super Bowl, only to lose to the Kansas City Chiefs both years.

However, when Bosa tore his ACL two games into the 2020 season, the 49ers finished the year 6-10, missed the playoffs, and finished last in the NFC West.