Williams left the game in first half and did not return.
The Texans would not speculate on the severity of the injury or how much time -- if any -- Williams could miss.
Williams appeared to be hurt while sacking Jason Campbell with about five minutes left in the first quarter of Houston's 25-20 loss to Oakland.
He was taken to the locker room and did not return. Coach Gary Kubiak offered no specifics on Williams' condition after the game.
"I'm not a doctor, so I don't know," Kubiak said. "I hate to answer that right now in the state of mind I'm in. So let's see what happens. I'll get back with you when I find out."
Williams, the top overall pick in the 2006 draft, moved from defensive end to linebacker this season in Houston's new 3-4 defense. He has five sacks and a forced fumble this season.
"He said he felt like something popped, but I don't know," defensive end Antonio Smith said. "The only thing that concerned me was that he didn't come back."
Williams' injury created more playing time for rookie Brooks Reed, a second-round draft pick. Reed had four tackles in Sunday's game.
"Initially, I've got to say that he looked pretty impressive," Kubiak said. "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," Kubiak said, "but that's what he's here for."
The Associated Press contributed to this report.