PITTSBURGH -- The Pittsburgh Steelers are feared to have lost another key piece of their vaunted defense.

Outside linebacker Bud Dupree, who appeared to injure his left knee on a noncontact play in the second half of Wednesday's 19-14 victory over the Baltimore Ravens, is believed to have suffered a torn ACL, a source told ESPN's Jeremy Fowler, confirming an NFL Network report. The severity of the injury is expected to be confirmed with further testing Thursday.

Dupree, 27, limped off the field following the injury and did not return to the game.

"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," wide receiver JuJu Smith-Schuster said, describing the Steelers' locker room after the game. "But that's something that, you always pray for everybody to be safe and have a healthy game."

Playing on the one-year franchise tag, Dupree will be a free agent after this season. He followed up his breakout 2019 campaign with another strong effort this season, recording eight sacks and two forced fumbles along with 26 tackles. Along with T.J. Watt, Dupree was a foundational piece of the Steelers' pass rush.

Replacing Dupree won't be easy. Rookie Alex Highsmith, the Steelers' third-round draft pick, is the top candidate to fill his role.

If the injury to his ACL is confirmed, Dupree would be the second Steelers defensive starter to go down with such an injury, after middle linebacker Devin Bush tore his against the Cleveland Browns.