"I think he's doing well," O'Brien said. "I think we've got a good plan in place for him from a medical perspective ... little bit more every day. He wants to be in there more, which is a great sign. It means he's probably feeling pretty good. ... We'll just keep inching him forward to be able to go in that first game."
Clowney, a second-year linebacker, returned to practice Aug. 17 after a lengthy recovery from microfracture surgery.
"I'm having fun out there now," he said. "Hitting everybody. Talking junk. That's what I do. I love it."
Clowney will not play in the Texans' third preseason game Sunday against the New Orleans Saints as the team follows a plan for his return dictated by its medical staff.
"I'm rusty," Clowney said. "I'm just trying to get as many reps as I can. Tell coach to put me in as much as possible. They're not trying to rush me back. Working me in slowly. I'll still be trying to get as many reps as I can so I can get ready for the game."
Clowney initially injured his right knee during the Texans' 2014 season opener. He had arthroscopic knee surgery for a lateral meniscus tear the next day. That surgery didn't turn out to be enough.
Clowney attempted to play in three other regular-season games, but his knee was not reacting well due to articular cartilage damage. He then had microfracture surgery early in December.
"We're on a schedule right now," Clowney said. "We talk about the schedule and we're going to keep to that schedule."