Pittsburgh Steelers first-round pick Derrick Harmon has sustained a medial collateral ligament (MCL) sprain and is expected to be sidelined, sources confirmed to ESPN.

The recovery timeline from an MCL sprain varies with the degree of severity, but it can generally take several weeks to a month for a player to return. That could make the defensive lineman a candidate for short-term IR, which would make him eligible to be activated after the team’s Week 4 game against the Vikings in Ireland. The Steelers have a Week 5 bye and face the Jets, Seahawks, Patriots and Vikings before the break.

Harmon sustained the knee sprain, which was first reported by NFL Network, when he appeared to fall awkwardly trying to get to quarterback Jack Plummer in the second quarter Steelers’ preseason finale against the Panthers on Thursday night. The injury appeared serious when he was taken back to the locker room in a cart with a towel draped over his head. Harmon, though, was back on the bench by the fourth quarter, laughing as he sat with teammates.

Coach Mike Tomlin said after the game Harmon had a knee sprain “of some description” and would be further evaluated. Additional imaging Friday revealed the MCL sprain.

Harmon, selected No. 21 overall in April’s draft, had a strong training camp after being tabbed a starter in minicamp alongside Keeanu Benton and veteran Cam Heyward in the team’s base defense.

“He’s heavy-handed, he’s competitive, he’s exactly what we thought he was,” Tomlin said during training camp. “Certainly he’s still very much a work in progress, getting acclimated, not only to the professional game, but specifically the things that we’re asking to do within our scheme.”

Fellow rookie Yayha Black, who had two sacks, a quarterback hit and two tackles for loss, against the Panthers, could be asked to be a bigger contributor with Harmon sidelined.

“We like Yahya’s progress,” defensive coordinator Teryl Austin said last week. “He’s not a little man, and when he really learns how to use all the tools at his disposal, he’s going to be a load inside.

“I like what he’s doing. He’s got a really good motor for a big man. … He’s trending in the right direction. When you compare him to [veterans]they’re going to have him in terms of how they read scheme, how they see different things. When you just look at the physical ability he has, you are pleased.”

Harmon’s absence could also impact Heyward as the veteran defensive lineman seeks to adjust his contract with raise in compensation for the 2025 season. The 36-year-old longtime captain briefly held in during training camp, but he returned to practice earlier this week and participated in some team periods.