Houston Texans star linebacker Mario Williams is out for the season with a torn pectoral muscle, according to a report.

Williams -- who transitioned into a linebacker after years as a defensive end -- suffered the injury during the first quarter of the team's loss to the Oakland Raiders. After the game there was speculation that Williams might be out for the season, but Texans coach Gary Kubiak wasn't sure of the extent of the injury.

I'm not a doctor, so I don't know, coach Gary Kubiak said following Sunday's game. I hate to answer that right now in the state of mind I'm in, so let's see what happens.

Williams underwent a MRI on Monday, which The Houston Chronicle's John McClain reported as a torn pectoral muscle -- ending his season.

The former No. 1 draft pick had five sacks on the season and is arguably the most important and talented defensive player on the Texans roster. The Texans are expected to replace the 6th year star with rookie Brooks Reed.

I think initially I got to say that he looked pretty impressive, Kubiak told reporters after the game. Looked like he had some good rushes off the edge.  He went from playing 10, 12 plays, to all of a sudden he probably played 50 in the game.  It's gonna be time for him to step up now, but that's what he's here for.  He's been doing some good stuff.

The injury marks the second injury to a key player in the last two weeks. Andre Johnson suffered a hamstring injury last week, in which he collapsed to the ground as if he were shot, while Arian Foster has also dealt with the injury bug all season.