Schaub is gone for the season with a right foot injury suffered in Houston's win over Tampa Bay last Sunday. He met with several doctors, including a specialist in Charlotte, who determined he'll need season-ending surgery on the Lisfranc injury.
Matt Leinart will start for Houston (7-3) in Jacksonville (3-7) on Sunday. Clemens becomes the backup and rookie T.J. Yates, a fifth-round pick, is No. 3 on the depth chart.
Clemens tried out for the Texans on Monday, along with Jeff Garcia, Trent Edwards, Brodie Croyle and Chase Clement. Clemens had an edge because he was in training camp with Washington and coach Mike Shanahan, Houston coach Gary Kubiak's former mentor.