Pittsburgh Steelers' first-round pick Derrick Harmon is expected to be sidelined for about a month with an MCL sprain, sources told NFL Network's Ian Rapoport.

The injury makes the defensive tackle a candidate to begin the season on injured reserve, Rapoport adds.

Harmon suffered the injury during the team's final preseason game against the Carolina Panthers on Thursday night. He was carted to the locker room after his knee twisted awkwardly on a pass-rush snap. However, he later returned to the sideline in street clothes.

The 21st pick in this year's draft, Harmon was expected to open the campaign as a starter on Pittsburgh's defensive line.

With Harmon sidelined, the Steelers could turn to the likes of Isaiahh Loudermilk, Daniel Ekuale, or rookie Yahya Black to fill in on the defensive line.