SANTA CLARA — Nick Bosa helped the 49ers to a 3-0 start this season, starting with strip-sack heroics that sealed win No. 1 in Seattle. Now they must try winning without their star defensive end every week for the rest of this season.
Bosa sustained a clean tear of the anterior cruciate ligament in his right knee during Sunday’s 16-15 home-opening win over Arizona, thus requiring season-ending reconstructive surgery and likely a year’s worth of grueling rehabilitation.
“I was told it’s as clean as it gets. So if you have an ACL (tear), it’s the kind that you want,” coach Kyle Shanahan said Monday on a conference call with reporters.
Sideline tests Sunday on Bosa’s ACL did not indicate it was torn, but Shanahan cautioned after the game: “We can’t rule anything out.”
Indeed, Bosa knew something was amiss. This injury is not new to him.
Bosa tore the ACL — plus his medial collateral ligament and meniscus — in his left knee two games into the 2020 season, or exactly five years and a day from this simpler ACL tear. He previously tore the ACL in his right knee during his senior year at St. Thomas Aquinas High (Fort Lauderdale, Florida) before going off to Ohio State.
“Obviously he was bummed out from not being able to finish out the year, especially how good a year he’s been having so far,” said Shanahan, who spoke Sunday night with Bosa, who rebounded from his 2020 ACL tear to win 2022 NFL Defensive Player of the Year honors,
Sunday’s fateful play was a third-down pass rush late in the first quarter. Bosa’s right knee did not draw noticeable impact, even though he eventually got floored on a double-team block.
Shanahan did not ask Bosa to relive how the injury occurred — the first torn ACL in an NFL game this season — but the coach noted: “That’s just how those happen a lot with ACLs, they happen on air. It got caught (in the grass) and went right away. A guy who’s done it two times before, he was pretty confident he did it.”
Upon limping to the 49ers’ sideline, he was examined on his back by medical staff, then gave a thumbs-down signal to his parents in a suite as he headed into the sideline medical tent. Bosa eventually walked to the locker room before halftime and he walked out after the game with a support sleeve on his right leg, while his father, John, carried his bag.
Bosa turns 28 on Oct. 23. He not only won DPOY honors in 2022 and NFL Defensive Rookie of the Year in 2019, he’s made the Pro Bowl in every season except his ACL-stricken 2020 campaign.
“Anytime you lose a guy like Nick, it’s a real buzzkill,” left tackle Trent Williams said after the game. “… It’s cliché to say it’s a next-man-up league. When you lose a guy like that, you need three or four guys to come and fill those shoes. We’ve got the depth. We’ve got the youth. So hopefully they can continue to improve.”
Bosa, a seventh-year veteran, was the only starting defensive lineman retained this past offseason as the 49ers poured draft resources into a revamped unit that includes rookies Mykel Williams (first round), Alfred Collins (second round) and C.J. West (fourth round). West may not be available this week, however, because of surgery required to repair a fractured thumb from Sunday, Shanahan said.
Bryce Huff, acquired in a June trade from the Philadelphia Eagles, has complemented Bosa well as the other pass-rushing end, but the 49ers also will lean more on Sam Okuayinonu and Yetur Gross-Matos, the latter of whom has rarely practiced because of a knee injury dating to the 2024 preseason. Trevis Gipson, a sixth-year veteran, and former 49ers draft pick Robert Beal Jr. are on the practice squad.
“Everyone has to continue to get better at everything. Same thing I’d be preaching if I had Nick, too,” Shanahan said.
“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 of Sunday’s winning formula. “So when we lose him, everybody has got to raise their game.”
Three 49ers players are coming off ACL reconstruction: wide receiver Brandon Aiyuk, safety Malik Mustapha and quarterback Kurtis Rourke. All are eligible to resume practicing after the 49ers’ next game, Sunday against Jacksonville, although it’s more likely that the earliest debut would come from Brandon Aiyuk in Week 6 at Tampa Bay, following a Thursday night, Oct. 2 game at the Los Angeles Rams.
Bosa recorded a sack in each of the 49ers’ first two games, and his strip-sack fumble recovery sealed the 49ers’ season-opening win at Seattle. Bosa did not comment to the media after the game nor was he made available Monday.
Financially, Bosa signed in 2023 what then was the richest contract for a non-quarterback (five years, $170 million). That contract runs through 2028, and Bosa counts $20.4 million against this season’s salary cap, behind only left tackle Trent Williams ($21.1 milion).
Bosa’s injury is the biggest amid a wave this season for the 49ers, who saw quarterback Brock Purdy (toe, left shoulder) and George Kittle (hamstring) get hurt in the opener. Wide receiver Jauan Jennings (ankle), guard Ben Bartch (high-ankle sprain) and offensive tackle Spencer Burford (knee) got hurt in the Week 2 win at New Orleans.
Purdy might return next Sunday against Jacksonville, though Shanahan said it’s unknown whether his franchise quarterback will be limited in Wednesday’s practice as he was all last week. Mac Jones, who won his two starts in place of Purdy, aggravated a knee sprain Sunday and is considered day-to-day.
Kittle is on Injured Reserve for at least two more games. Burford and Bartch last week went on Injured Reserve, where the 49ers put eight players during training camp, including running back Patrick Taylor Jr.
Should the 49ers scour around the league for defensive end, the trade deadline is Nov. 4, and likely the most popular player will be Cincinnati’s Trey Hendrickson, who is playing on a one-year, $29 million deal after failing to secure a multi-year extension prior to the season.
“We’ll look at trades like we always dom” Shanahan said. “But, there’s got to be trade options that make sense for you and another team. You can’t just do that stuff just to do it.”
Originally Published: September 22, 2025 at 11:47 AM PDT