McKnight has a new injury

The misadventures of USC running back Joe McKnight continue.

The sophomore from Louisiana spent Sunday night’s practice on a golf cart, wearing a near full-length brace on his right arm. McKnight suffered a hyperextended elbow in the Trojans’ scrimmage at the Coliseum the night before, Coach Pete Carroll said.

McKnight’s latest mishap came only a few days after he injured two fingers, including a slight fracture at the tip of one, when a teammate accidentally closed a dormitory door on McKnight’s right hand.

McKnight sat out parts of a few practices after that mishap. He was previously sidelined because of a skin irritation.

McKnight declined to comment Sunday.

“It’s unfortunate, Joe keeps coming up with something,” Carroll said, adding that McKnight could miss a few workouts.

“He has missed a lot of practice already and it’s killing him. He hates the fact that he has. The fingers are fine, he’s ready to go, but something else popped up.”

McKnight sat out on a night when several players returned from injuries, including tight end Blake Ayles and offensive linemen Alex Parsons and Tyron Smith.

Carroll said he did not know how long cornerback Cary Harris would be out because of a dislocated right shoulder suffered during the scrimmage.

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Quarterback battle intensifies

With less than two weeks before the Aug. 30 opener against Virginia, the quarterback derby is moving into a pivotal stretch.

Aaron Corp and Mitch Mustain are competing to possibly replace injured starter Mark Sanchez, while Sanchez is working to return in time to play against the Cavaliers.

“I haven’t taken any steps back in my rehab so everything is looking good right now, but we’ll have to wait and see,” said Sanchez, who suffered a dislocated left kneecap 10 days ago.

Carroll said Sanchez was expected to do some running on the field Tuesday and that other elements would be added as he progressed.

Knowing who the starter might be heading into game week was not imperative, according to Carroll.

“Everything is still up in the air and we’ll just see,” he said. “There’s no rush yet.”

Both Mustain and Corp said they felt better about their performances in the scrimmage after reviewing film Sunday.

Carroll spent about five minutes on the field after practice talking with Corp.

Asked what they spoke about, Corp said Carroll told him, “Keep working on making plays.”

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Coming and going

Excuse offensive lineman Zack Heberer if he occasionally hesitates before lining up on the right or left side of the center.

With senior Jeff Byers’ status having been uncertain, Heberer had flip-flopped between right and left guard throughout training camp.

“It doesn’t matter to me,” Heberer said. “It’s better to be diverse.”

Heberer is expected to return to right guard full-time starting today. Carroll said Byers, who did not play in Saturday’s scrimmage, has been cleared to participate in all drills.

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Quick kicks

Junior linebacker Nick Garratt was awarded a scholarship. . . . Players will move out of the team dormitory today and into their regular housing on and off campus. . . . The team practices today at 4 p.m.

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gary.klein@latimes.com