Wide receiver Mario Manningham left the 49ers' game against the Seahawks in the third quarter with an apparent left knee injury and will not return.
Manningham caught a short pass from Colin Kaepernick and fumbled the ball after a hit forced him into an awkward position.
The Seahawks recovered the fumble and Manningham was helped off by team trainers.
Manningham was returning to action after missing the previous two games with a shoulder injury. He was transported back to the 49ers’ locker room on a cart for further evaluation
Tight end Vernon Davis left the game earlier after sustaining a concussion.