Monday night, as Oklahoma’s players lined up to run post-practice sprints, linebacker Ryan Reynolds started doing crunches. That’s what injured players do when they can’t run.

The linebacker’s energy caught Sooner coach Bob Stoops a little off guard.

“I picked him up off the ground and said, ‘What are you doing?’” Stoops said. “Usually the guys that can’t run do something else. I told him we would give him an exception.”

Fact is, Monday’s practice was all about figuring out what OU will do without Reynolds. The junior middle linebacker suffered a season-ending knee injury in Saturday’s 45-35 loss to Texas. Figuring out his replacement will be the biggest personnel question the Sooners may face this season.

Reynolds’ impact on OU’s defense went well beyond his production in terms of tackles. Both strongside linebacker Keenan Clayton and weakside linebacker Travis Lewis are first-year starters. They leaned on Reynolds whenever questions arose in the heat of a game.

“That’s why my head is aching. I’m doing a lot more thinking right now.” Lewis said Monday. “I’m so used to Ryan making the calls and me just lining up and playing football.”

There hasn’t been a definitive shift in the depth chart heading into Saturday’s game against No. 16 Kansas. Defensive coordinator Brent Venables said Mike Balogun and Brandon Crow, who were Nos. 2 and 3 on the middle linebacker depth chart heading into the Texas game, will get a shot at the job.

But the most likely scenario will be to move Austin Box, who backed up Lewis at weakside linebacker, to the starting middle spot.

“I’m really excited about it. It’s very disappointing with the way it had to happen. I know there’s a good possibility my number will get called. I feel I’m ready,” Box said Monday. “If I switch over to the mike [middle linebacker], it’s not like it’s a completely foreign language to me. I’ll be able to pick it up fairly quick. I’m excited for the opportunity to help the team out.”

Box has proven capable of being a starter. He entered the preseason as the projected starter at the weakside spot. An injury kept him on the sidelines until the Cincinnati game. By then, Lewis had already proven himself to be an emerging star. His 19-tackle performance against Texas is in indicative of how he’s playing. OU doesn’t want to do anything to hamper his production.

Whether it’s Box, Balogun or Crow, no one will be asking them to cram a year’s worth of experience into the next four practices.

“When the coach calls your number and puts you in that position, you have to step up and make those plays,” Lewis said. “Learning the game plan for the week is easier than learning the overall defense. If you can get the game plan down for the week, you can play the position.”

But it’s become clear the Sooners are out of patches if the situation gets worse. Even Venables admits the loss of Reynolds is a major blow to a unit that entered the year light on experience and lighter on depth.

“We lost the one (player) we really couldn’t afford to lose because of the youth of the group,” he said. “Losing guys like (Curtis) Lofton and Mike Reed not working out really caught up to us when you lose Ryan as well.”

Still, a scary thought for OU is replacing one linebacker with another at less than full strength. Box had arthroscopic knee surgery in August and missed the second half of spring practice due to a dislocated elbow.