Houston Texans linebacker Mario Williams will undergo season-ending surgery after tearing a pectoral muscle in Sunday's loss to the Oakland Raiders, Texans coach Gary Kubiak said on Monday.

Williams, the National Football League's (NFL) top draft choice in 2006, was injured during the first quarter after sacking Raiders quarterback Jason Campbell.

He's done for the season, Kubiak told reporters.

Williams will be placed under injured reserve and have surgery in the next week.

He was shifted from defensive end to linebacker as an experiment this season, and Kubiak said he had really taken to the position.

He was improving every day at practice, improving in every game and really enjoying, the coach said. I've never seen him so upbeat about what was going on and then to lose him on a freak play.