NORMAN, Okla. (AP) — As No. 16 Oklahoma enters the heart of its Big 12 Conference schedule, the Sooners suddenly find themselves thin at a key position.

Coach Bob Stoops said Monday that standout junior running back Samaje Perine - who entered the season within striking distance of the program's career rushing record - will miss at least the next two games due to a "slight pulled muscle" in his left leg.

Oklahoma (4-2, 3-0 Big 12) still has another proven runner in sophomore Joe Mixon for its game Saturday at Texas Tech (3-3, 1-2). But the only healthy running back on the roster behind Mixon is seldom-used freshman Abdul Adams.

Stoops described Perine's injury situation as "ongoing. A running back with a slight pull, we've just got to make sure that it heals properly. That will be here for a couple of weeks, for sure."

After facing Texas Tech, Oklahoma will host league cellar-dweller Kansas on Oct. 29, then visit Iowa State on Nov. 3 before hosting No. 9 Baylor on Nov. 12.

The 5-foot-10, 235-pound Perine has been durable for the Sooners throughout his career, battling through earlier injuries and never missing a game. He entered the season 1,056 yards shy of Billy Sims' career rushing record of 4,118 yards, and now is seventh on Oklahoma's all-time list with 3,537 yards. This season, he's rushed for 475 yards - 214 of those in a win over Texas - and scored seven touchdowns.

But after scoring the Sooners' first touchdown in their 38-17 win over Kansas State on Saturday, Perine hobbled off the field and didn't return.

Perine's absence is more pronounced because the Sooners already have lost two running backs this season. Rodney Anderson, expected to compete for time behind Perine and Mixon, suffered a preseason neck injury and won't play in 2016, while Daniel Brooks decided to retire from football earlier this month due to concussions.

The 6-foot-1, 226-pound Mixon, who has rushed for 476 yards and two touchdowns this season, certainly is capable of carrying a bigger load for the Sooners. Adams has played in only two games and is an unknown quantity. He had six carries for 11 yards against Kansas State.

"He's come on, been more consistent," Stoops said of Adams. "He did a nice job in there the other day of being correct with all of his assignments and everything. . He's a good solid player and he's going to have more opportunities obviously now."

Stoops said Perine's injury will have an effect the play-calling by offensive coordinator Lincoln Riley.

"It influences everything," Stoops said. "Joe and Samaje together are a great team in keeping each other fresh and they're both so reliable, you (can) really interchange plays where you don't care which ones in there. Obviously Joe will have more of a workload and knowing him, he'll like that. We'll have to be smart and coach Riley is a very bright guy in how we manage them both."

For the time being, Mixon won't also return punts for the Sooners, helping keep him fresh for added running duties. Wide receiver Dede Westbrook will move into the punt-return role, Stoops said. Should Mixon or Adams go down, Stoops said a fullback, such as junior Dimitri Flowers, could see some carries.

"We'll pay attention to that here this week, some of the other offensive players who might have a chance," Stoops said.