Steelers linebacker Bud Dupree tore his left ACL in Wednesday's 19-14 victory over the Ravens, according to NFL Network's Ian Rapoport.
On Thursday, an MRI reportedly confirmed initial fears of Dupree's injury.
The non-contact injury occurred in the second half of Wednesday's win. Dupree limped off the field following the injury and did not return to the contest.
"I think it was very quiet, very sad, very low, just because having our fellow teammate going down, Bud, and not knowing what's going on over there," Steelers wide receiver JuJu Smith-Schuster said after the game.
Dupree has spent the 2020 NFL season playing on the franchise tag and the 27-year-old linebacker is slated to be a free agent this offseason.
He entered Week 12 with eight sacks, the fifth-most sacks in the NFL, and two forced fumbles along with 26 tackles. Dupree added five tackles and two tackles for loss against the Ravens.
Dupree becomes the second Steelers defensive starter to suffer a torn ACL this season. Linebacker Devin Bush tore his ACL against the Cleveland Browns in Week 6.
With Wednesday's victory, Pittsburgh moved to 11-0 on the season. The Steelers play the Washington Football Team on Monday evening.