"You've just got to do what's best for Mario," Kubiak said. "I'd have loved for him to be able to hang in there and give us 20 to 25 plays a game the rest of the way, but he just wasn't getting better. It was getting worse, and the last two weeks have been the worst. The doctors just feel like he needs to get this fixed right away."
Williams has started every game in his career -- 77 in a row. He has 28 tackles, 8.5 sacks and a forced fumble this season.
"Mario is a tough guy, gives his team everything he has," Kubiak said. "Even when he's not 100 percent, he's a dang good player. So there's a lot to be said for what he's been doing and especially what he did this year."
Williams wasn't available for comment Wednesday.
"He was fighting, and you could just tell that he was in a lot of pain," Smith said. "It was hard to play with. It hindered him in this last game to the point where I knew it was something seriously wrong. After one play, he just stopped and ... said, 'Man I think something's really wrong.'"
Tim Jamison, who has appeared in seven games this season, will receive the majority of playing time in place of Williams, but Kubiak said a combination of people will fill his role.
The Houston Chronicle reported the team is expected to sign veteran defensive end Jarvis Green to help replace Williams.
The Texans also placed wide receiver David Anderson (shoulder) and guard Mike Brisiel (calf) on injured reserve. The Texans signed wide receiver Derrick Townsel from the practice squad to the active roster and added defensive tackle DeMario Pressley to the active roster from the New Orleans Saints' practice squad.
The Associated Press contributed to this report.