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The 49ers on Monday got the news they feared most: An MRI showed that edge rusher Nick Bosa tore his ACL during Sunday’s win over the Arizona Cardinals. Bosa, the NFL’s defensive player of the year in 2022 and league leader in pressures ever since he joined the 49ers in 2019, will require surgery and miss the rest of the 2025 season.
ESPN’s Adam Schefter reported that Bosa suffered a clean tear, meaning no other ligaments were damaged.
While that’s a silver lining and indicates that Bosa should be back for the start of the 2026 season, this is obviously gut-punching news for the 49ers. But the 16-15 win over the Cardinals does provide at least some hope for the team moving forward. That’s because the defense, after completely collapsing the moment Bosa went down with an oblique injury in 2024, actually held strong without its superstar.
Can the 49ers sustain Sunday’s success by leaning more heavily into their hard-charging group of youngsters on defense?
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There are indications that defensive coordinator Robert Saleh might be able to replicate at least some of what he accomplished after Bosa tore his other ACL back in 2020. That season, Saleh’s defense managed to finish No. 6 in DVOA (defense-adjusted value over average). Through three games in 2025, the 49ers’ defense again ranks No. 6.
In 2020, Saleh significantly upped the 49ers’ blitz rate after Bosa went down. He developed creative pass-rushing combinations with line coach Kris Kocurek and focused on complex coverage disguises with the secondary.
While the 49ers’ defense wasn’t nearly as dominant as it had been the season prior with Bosa, it remained a good unit. It even saw journeyman defensive lineman Kerry Hyder Jr. rack up a career-high 8.5 sacks in Bosa’s place.
The 49ers are significantly younger this season than they were in 2020, but that means there is more moldable clay for Saleh and Kocurek to work with. The season’s first three wins suggest that the team — which spent its first five 2025 draft picks on defensive players — should enjoy significant growth thanks to its large share of developing youth.
First-round pick Mykel Williams logged a team-high six pressures against Arizona. Fellow draftees Alfred Collins and CJ West both shouldered their biggest snap loads yet. And on a symbolically significant play, the rookie trio combined to pressure Arizona QB Kyler Murray into an intentional grounding penalty that was nearly also a safety.
“When I got up and looked around, I realized it was me, AC, and CJ,” Mykel Williams said in the locker room. “I was like, ‘Damn. All of us are out here making plays?’ And it just turned me up. Gave me good energy.”
The Bosa injury news, of course, threatens to drain many of Sunday’s positive vibes. He’s just that great of a player. But it’s incumbent on Saleh and the rejuvenated pool of young talent to pick up as much slack as possible — especially because there is clearly ability in the room beyond that rookie class.
Veterans Yetur Gross-Matos and Bryce Huff are both off to strong starts. Huff has been especially impressive the past two weeks. The pass-rushing specialist saw an expanded role after Bosa exited the game and managed to even deliver well against the run.
Ultimately, the 49ers’ biggest hope without Bosa lies in their offense — the unit that had been expected to carry this team before the defense’s surprisingly strong start to 2025.
The 49ers have been beaten up on the offensive side of the ball, but quarterback Brock Purdy and receiver Demarcus Robinson (who finished serving his three-game suspension) should return this week. George Kittle, Jauan Jennings, and Brandon Aiyuk shouldn’t be too far behind them.
A top-five offense paired with just an average defense would keep the 49ers in contention. And beyond that, the 49ers have room to make additions. The NFL trade deadline isn’t until Nov. 5, and some teams may enter fire-sale mode in the next six weeks.
Remember the name Kayvon Thibodeaux of the New York Giants — who are 0-3. A player such as Thibodeaux, or perhaps the Tennessee Titans’ Arden Key, could be called on as the 49ers explore ways to pick up the slack created by Bosa’s injury.
The 49ers aren’t doomed yet, especially because they’ve already socked three wins into the bank.
That’s why star left tackle Trent Williams was thinking about Bosa during Sunday’s game-winning drive. He understood that the edge rusher’s injury added to the importance of securing that victory.
“When you lose a guy like that,” Williams said, “you need three or four guys to come and fill those shoes.”