Manning was injured in Sunday's loss to St. Louis. Coach Gary Kubiak called it a significant injury Monday but didn't have any further details on the injury Wednesday.
Shiloh Keo will fill in for Manning. Keo, a graduate of Archbishop Murphy High School, was a fifth-round draft pick in 2011 who spent time on the practice squad that year before appearing in 14 games last season.
The Texans also placed rookie cornerback A.J. Bouye on injured reserve Wednesday with a right hamstring injury. Bouye had played mostly special teams this season.
Houston signed cornerback Elbert Mack and linebacker Mike Mohamed to take their spots on the roster.
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