Clowney was hoping to make his return from a knee injury in Monday's game. The rookie tore the meniscus in his right knee in the second quarter of Houston's season opener against the Washington Redskins on Sept. 7. He had arthroscopic surgery a day later.
On Wednesday, Texans coach Bill O'Brien said there was a 50/50 possibility of Clowney playing against Pittsburgh.
Clowney was limited to conditioning work during Thursday's practice. Earlier Monday, NFL.com's Aditi Kinkhabwala reported that the rookie was working out at Heinz Field and running hard cross field sprints.
Monday marks six weeks since Clowney's surgery, and team officials had said he would need four to six weeks to recover.
Whitney Mercilus is expected to start again in place of Clowney. Mercilus has 19 tackles this season.
The Texans and Steelers are both 3-3 heading into Monday Night Football.
- Molly Geary