The San Francisco 49ers just can’t catch a break when it comes to fielding a healthy roster.

Star receiver Brandon Aiyuk is still recovering from a torn ACL and MCL, All-Pro tight end George Kittle is on injured reserve, and starting quarterback Brock Purdy and receiver Jauan Jennings both missed Sunday’s game against the Arizona Cardinals, and now the team may be looking at the prospect of being without its best defensive player for a decent chunk of time.

All-Pro edge-rusher Nick Bosa left Sunday’s 16-15 win over the Cardinals late in the first quarter with an apparent knee injury.

More NFL: Buccaneers Announce Troubling Mike Evans Update After Win Over Jets

No details were made public regarding how severe Bosa’s injury is, but head coach Kyle Shanahan revealed what happened immediately after the injury that has him concerned.

“They haven’t ruled [an ACL injury] out, no — we’re not sure,” Shanahan told reporters. “There is concern because of how he feels, and they did a test and stuff on the sideline and usually they say whether he definitely did [tear it] or not, and they didn’t say that. But we are concerned [about an ACL injury], and we’re keeping our fingers crossed for the MRI.”

More NFL: Steelers-Tyreek Hill Trade Rumors Get Major Update

More NFL: Browns Close to Making a Quarterback Change: Report

After getting to the sideline following the injury, Bosa immediately fell to the ground. On his way to the blue medical tent, Bosa looked at the crowd and gestured with a resounding thumbs down.

49ers offensive lineman Trent Williams stated he spoke to Bosa in the locker room after the game and described the situation as a “buzz kill.”

If it is indeed an ACL injury, it’ll mark the second time in his NFL career that particular injury has cut his season short.

During his second year in the league back in 2020, Bosa missed the final 14 games of the 49ers’ season after suffering a torn ACL in a Week 2 game against the New York Jets.

After a lengthy recovery, Bosa returned the following season and posted one of the better seasons of his career, totaling 88 pressures, 50 hurries, 17 QB hits, and 15.5 sacks, according to Pro Football Focus.

More NFL: Eagles’ Staffer ‘Big Dom’ Hit With Massive Fine by NFL