The club announced Monday an MRI confirmed the left knee injury he suffered during Week 2 against the New York Jets. Ian Rapoport of NFL Network noted the injury will rule Bosa out for the remainder of the season.
The 2019 Pro Bowler was a revelation for the Niners in his first season, racking up 47 total tackles, nine sacks, one interception and one forced fumble en route to a Defensive Rookie of the Year award. San Francisco was expecting that stellar play to continue in his sophomore season.
Instead, he was carted off early in the first quarter of Week 2.
The former Ohio State star was one of four key Niners players injured against the Jets.
Quarterback Jimmy Garoppolo left the game with a high ankle sprain, running back Raheem Mostert suffered a mild MCL sprain, and defensive tackle Solomon Thomas exited with a knee injury.
With Bosa and Thomas sidelined, San Francisco will be hard-pressed to replicate the same pass rush that helped it reach the Super Bowl last season.