The Texans have placed inside linebacker Keyaron Fox on injured reserve and signed inside linebacker Omar Gaither.
Fox, a ninth-year veteran who was signed a day before training camp, suffered a left knee injury on Wednesday that will require surgery.
"Obviously sad for the kid; just got rolled up in a drill," Texans coach Gary Kubiak said. "I think he's been playing eight or nine years, so you hate to see that happen. But we'll take care of him, and he'll be a part of our team this year."
Gaither (6-2, 235), 28, was a fifth-round draft pick out of Tennessee in 2006. He spent last season with the Carolina Panthers after five seasons with the Philadelphia Eagles. Gaither has 40 career starts and led the Eagles with 100 tackles in 2007. He has 34 career special teams tackles.
Kubiak said Gaither will travel with the Texans to Carolina this weekend but will not play in the preseason opener. Mister Alexander, Tim Dobbins and undrafted rookies Shawn Loiseau and Greg Williams are the team's other backups to inside linebackers Brian Cushing and Bradie James.