Markey has his eyes on the end zone

Tailback Raymond Carter hobbled around on crutches at practice Thursday, his season over. The rest of UCLA’s tailbacks went back to work.

Carter, a promising freshman, is out for the season because of a knee injury, leaving the Bruins’ backfield -- which lost Derrick Williams to concussions in the spring -- down another man.

What remains are the top rungs on the depth chart, Chris Markey and Kahlil Bell, but the ranks thin out quickly. Chane Moline and walk-on Ryen Carew are the only safety nets.

“It’s a shame about Derrick, he was a warrior, and now we lost the rook,” Bell said. “But we still have a lot of talent and experience back there. We’re all up to the challenge.”

Markey, who gained 1,107 yards last season, gives the Bruins a quality starter, one who is pushed to prove wrong critics who question his breakaway speed.

“I have to be a playmaker this year,” said Markey, a senior. “I can’t just get the 20-yard runs. I have to get the ball into the end zone.”

Bell, who played in only seven games because of an ankle injury and a two-game suspension, could fill a more prominent role after adding 15 pounds.

“It has helped my speed and I feel more explosive,” said Bell, who weighs 219. “I’m more powerful. It’s where I should be.”

Bell was second on the team with 239 yards rushing last season.

Carew, meanwhile, took Carter’s reps during practice Thursday.

A date has not been scheduled for surgery to repair Carter’s torn anterior cruciate ligament. He was injured during a non-contact drill Tuesday.

“I was trying to cut and my cleat got stuck in the turf,” Carter said. “I didn’t think it was that bad at first. But a couple minutes later it started to stiffen up.”

Doctors will not know how long Carter will be out until after the surgery, but rehabilitation can take as long as nine months.

“I’m going to be ready by spring,” Carter said.

chris.foster@latimes.com