The franchise's all-time sacks leader is out for the season after being injured in last week's 25-20 loss to Oakland. Defensive coordinator Wade Phillips said the surgery "went well." Rookie linebacker Brooks Reed will replace Williams against the Ravens (3-1).
Reed, a second-round pick, was on the field for all but nine plays in last Sunday's game. Phillips said he'll scale back some of the calls that Houston (3-2) would normally play with Williams manning the outside linebacker position, but the coaches have quickly developed confidence in Reed.
"There's going to be a drop-off, obviously," Phillips said. "There's going to be some things you can't do that you could do with the other guy. But people are going to have to step up."
Phillips said one advantage for the Texans created by Williams absence is the unpredictability of Houston's blitz packages.
"There were certain things that we would run, that Mario was going to rush no matter what," Phillips said. "Now, we have some versatility that they (the Ravens) don't know who's going to rush and who isn't. That helps a little bit, but we'd rather have Mario.
"We just had some special things that we did with Mario and you're not going to be able to do those things," Phillips said. "But the rest of the stuff, like I said, we played in the ballgame (against Oakland) and I thought our group overall played pretty well."
Also, quarterback Matt Schaub practiced Friday after missing time earlier this week with a sore throwing shoulder. The Texans added Derrick Mason to boost the receiving corps without Andre Johnson, who's out this week with a right hamstring injury.
Johnson watched practice Friday with ice wrapped around his hamstring, and he gave no timetable for his return. He said he's "been getting better every day" since having minor surgery last week.
"I think, not only am I surprising myself, I think I've surprised a lot of people," Johnson said. "I'm just taking it a day at a time, trying to get better every day, trying not to have any setbacks. We haven't had any setbacks so far, so that's a positive thing."
Johnson was due to have more treatment on Saturday and was scheduled to run and test the hamstring on Monday. Houston plays at Tennessee next weekend.
"You definitely have to be very careful," Johnson said. "When I'm out there on the field doing little drills or things like that, they're always asking me how I'm feeling. Am I feeling any pulling or anything like that? The biggest thing is not having any setbacks, so that's the thing we're trying to stay away from."
Fullback James Casey (strained pectoral muscle) was the only Texan listed as doubtful for Sunday's game. Kubiak expects to have a full complement of healthy running backs -- Arian Foster, Ben Tate and Derrick Ward -- available in Baltimore.