Redskins running back Tim Hightower is helped off the field by trainers on Sunday. Monday he learned he would miss the rest of the season with a torn anterior cruciate ligament. (Ricky Carioti/WASHINGTON POST)

The Washington Redskins’ losses in the locker room are outpacing their woes in the standings, as two more key offensive contributors joined their growing list of injured players Monday.

Coach Mike Shanahan said that running back Tim Hightower tore the ACL in his left knee in Sunday’s 33-20 loss at Carolina and will be placed on season-ending injured reserve. Wide receiver Santana Moss should return this season, but he’ll be out five to seven weeks after undergoing surgery to repair a broken bone in his hand, Shanahan said.

As players reported to Redskins Park on Monday to regroup after Sunday’s sobering defeat to the Panthers, the team could have filled a small medical ward. Moss was preparing for surgery. Quarterback Rex Grossman had checked into an area hospital, where his peneumonia and high fever were being monitored. Hightower was undergoing an MRI exam that would confirm the worst fears about his knee. And tight end Chris Cooley was consulting with orthopedist James Andrews to discuss his future.

“You kind of go through some situations like this — hopefully not too often — where you lose a number of starters,” Shanahan said. “I don’t think I’ve ever lost so many just on one side so quickly.”

When the Redskins meet the Buffalo Bills this Sunday, they’ll have only four offensive starters from Week 1 healthy, starting and playing the same position they did on Sept. 11 against the New York Giants. John Beck has replaced Grossman at quarterback. Hightower and guard Kory Lichtensteiger are finished for the year. Left tackle Trent Williams is recovering from a high-ankle sprain sustained Oct. 16 against the Eagles. And Moss and Cooley both have pins holding together broken bones in their hands. Cooley will likely miss at least three more games. Former center Will Montgomery has moved to left guard.

“Any time you have, like, seven new starters from when you started, it’s always a little different,” Shanahan said. “On the good side, John Beck was practicing with the scout team and a lot of those players are out there now. So he’s comfortable with them.

“That was kind of a joke,” he added.

But only kind of. The Redskins will be looking for several young reserves to become contributors as the team tries to re-establish itself as a division contender. Nine days ago, the Redskins were in sole possession of first place in the NFC East. They’ve now lost three of their past four games and have two difficult opponents ahead: the Bills (4-2) and San Francisco (5-1).

“We have to win. That’s the nature of the game,” Shanahan said. “We have to find a way to win. The guys that will step up are guys that are going to be starters. They’re on our football team for a reason. Now, we have a chance to see what they could do.”

Running backs Ryan Torain and Roy Helu will likely share duties in the backfield. The Redskins will also need to add a third running back at some point this week and could promote rookie Evan Royster from the practice squad.

“You’ve got to be ready to come in and play whenever coach asks you to,” Torain said. “With his system, coach wants you to go in there and play like you’re the starter even if you’re third string. He prepares us for that mentality.”

While Torain is a strong runner, he hasn’t shown the blocking skills and ability to pick up blitzing linebackers that Hightower and Helu have. Helu could continue in his role as the team’s third-down back.

“He was playing so well in that game,” the rookie said of Hightower. “. . . But it’s another opportunity again, like any other position. So we have to come in and really pick up the slack.”

This will be the first season in Hightower’s four-year career that he is unable to play all 16 games. He started five of the Redskins’ six games this season and leads the team with 321 rushing yards and a touchdown on 84 carries. Acquired from the Arizona Cardinals in July, Hightower also has 10 catches for 78 yards and a touchdown.

“When you’re in a situation like [this] — you’re not able to help your team and you’re not able to do what you were brought here to do — it’s a terrible feeling,” he said after Sunday’s game.

With Moss and Cooley out, Beck will be without the Redskins’ two most prolific and reliable receiving targets over the past six years. Moss, who entered Sunday’s game leading all Redskins wide receivers with 22 catches for 284 yards and two touchdowns, had three pins inserted into his left hand, a similar procedure to the one Cooley underwent a week earlier.

“I know how this game is,” Moss said after Sunday’s loss. “I don’t let that stuff rattle me. I don’t like missing nothing. . . . Everything happens for a reason. Take it for what it is. Take it for how it is. Get it healed up and bounce back.”

Logan Paulsen will continue to see more action at tight end and wide receivers Anthony Armstrong and Niles Paul will need to play bigger roles on offense. The Redskins might also use Terrence Austin or Donte Stallworth in the slot, where Moss usually lined up.

The Redskins’ defense hasn't been decimated in quite the same fashion as its offensive counterpart, though the team’s training staff is closely monitoring some key contributors before deciding whether they can practice this week. Safety Oshiomogho Atogwe (hamstring) didn’t practice last week and was inactive in Charlotte. Linebacker London Fletcher missed the end of Sunday’s game because of a hamstring injury.

“How serious is it? I really don’t know,” Shanahan said. “I don’t think it’s that serious, but we’ll find out more on Wednesday.”

Staff writer Mike Jones contributed to this report.