49ers coach Kyle Shanahan announced star edge rusher Nick Bosa "most likely" tore his ACL on Sunday during San Francisco's 31-13 win over the New York Jets.
Bosa was carted off the MetLife Stadium turf during the first quarter. Defensive lineman Solomon Thomas was carted off on the very next play.
Shanahan said he believes Thomas also could be dealing with an ACL injury, but his prognosis appears better than Bosa's.
Quarterback Jimmy Garoppolo left Sunday's win with a high ankle sprain, and running back Raheem Mostert exited with what Shanahan called "knee issues."
Losing Bosa for the season would be a huge blow to the 49ers. He was named the NFL Defensive Rookie of the Year last season after recording nine sacks, 16 tackles for loss and 25 QB hits. Bosa added four more sacks in three playoff games.
Bosa started off this season strong, too, with six tackles, one QB hit and one forced fumble in the 49ers' Week 1 loss to the Arizona Cardinals.
Garoppolo completed 14 of 16 passes for 131 yards and two touchdowns, but that all came in the first half. Nick Mullens replaced the injured Garoppolo in the second half, and completed 8 of 11 passes for 71 yards with one interception.
Mullens likely will start in place of Garoppolo in Week 3 against the New York Giants.
The 49ers already entered Sunday without injured starters George Kittle (knee), Richard Sherman (calf), Dee Ford (neck) and Deebo Samuel (foot).