Riley also revealed that redshirt freshman defensive lineman Jordan Kelley has already undergone surgery for a lower-body injury.
"If there's a silver lining it's the timing of the injuries, with them occurring five months before the season," Riley said in a statement. "I know they'll work their tails off to get back to the field as quickly as possible, and we'll be there with them every step of the way."
Kelly started five games last season and finished fourth on the team with 61 tackles. He also returned a fumble for a touchdown at West Virginia in a victory that clinched the Sooners' spot in the Big 12 championship game.
Oklahoma will play its spring game April 13.