"I don't know, I really don't," O'Brien said when asked about Stills' availability. "I wish I could tell you. I think it's day to day. I definitely think it's day to day. He might be able to play Sunday."
Stills went down in the first quarter of the Panthers loss. He caught a pass on the right side of the field and stepped out of bounds early, hobbling.
Stills, who was acquired in a trade with the Miami Dolphins that also included left tackle Laremy Tunsil, has 11 catches on 13 targets for 188 yards and a touchdown this season, He is the only Texans wide receiver other than DeAndre Hopkins with a score this season.
Just before the Panthers game, the Texans lost right guard Zach Fulton to back tightness. They started Greg Mancz in his place and it did not go well.
This also forced the Texans to start their fourth different offensive line in as many weeks.
O'Brien said he felt better about Fulton's status.
"I feel good about Zach," O'Brien said. "I think it's day to day but I think he'll have a shot."