CINCINNATI -- Bengals linebacker Nick Vigil has an MCL sprain and is expected to miss about a month, according to a source.

Vigil injured his left knee following a cut block by Steelers fullback Roosevelt Nix. Vigil went to the ground and stayed there for a few moments before trying to get up and hop to the sideline. He fell to the ground again before athletic trainers came out to assist him, and then he immediately went to the locker room. Vigil was quickly declared out.

Vigil walked through the locker room on Monday morning wearing a large knee brace and using crutches. The Bengals could also be down several other defensive players this week, as Darqueze Dennard had his shoulder in a sling on Sunday night and Shawn Williams is in concussion protocol.

Vigil was the Bengals' defensive signal caller and ranked sixth in the NFL with 51 total tackles. He was replaced by Bengals veteran linebacker Vincent Rey, who has backed up all three linebacker positions at times for Cincinnati. Jordan Evans or Hardy Nickerson could be candidates to play in Vigil's place next week as well.

"Nick has really improved as a football player from last year. Really has a good understanding of football. What he gives you is he gives you a long, athletic linebacker, almost like a big strong safety who can play in the box, he can cover tight ends, he's good with backs," said Bengals defensive coordinator Teryl Austin. "That's the stuff you'll miss with him. A guy that you can match up with different types of guys, different core guys, and he's pretty effective with all of them. And he was our helmet communicator. So I'll be talking to somebody different this week."

The NFL Network first reported the news.