A Washington Redskins defense that has struggled through two games will be without a pair of key performers for the remainder of the season. Outside linebacker Brian Orakpo and defensive end Adam Carriker are finished for the year after being injured in Sunday’s loss at St. Louis.

Orakpo suffered a torn left pectoral muscle and Carriker suffered a tear of the quadriceps tendon near his right knee, Coach Mike Shanahan said. Each player will undergo surgery. Carriker faces a five-month recovery period and Orakpo is to spend close to four months recovering from his injury, Shanahan said.

The losses of Orakpo and Carriker mean the Redskins could be without four defensive starters Sunday when they play their home opener against the Cincinnati Bengals.

Cornerback Josh Wilson left the game in St. Louis with a concussion, and under NFL rules he must be cleared by an independent neurologist before being allowed to practice or play. It also was unclear whether safety Brandon Meriweather, who has missed the first two regular season games with a knee injury, would be ready to return to the lineup.

The loss of Orakpo could be particularly troublesome. He had one sack in two games this season after leading the Redskins with nine sacks a year ago. The former first-round draft choice from Texas had 281 / 2 sacks in his three previous NFL seasons.

“Obviously he’s a guy that can do it all,” Shanahan told reporters. “He can cover. He can rush. He can play the run. He’s a very physical, very smart; team player. He’s all the things you look [for] in a Pro Bowl player. And obviously we’ll miss him.”

The Redskins hoped to have one of the league’s top defenses this season but they were ranked, entering Monday night’s play, 28th in the NFL in total defense. They were 27th in scoring defense and 30th in pass defense.

Orakpo left the field early in Sunday’s 31-28 defeat to the Rams, after sacking quarterback Sam Bradford to end St. Louis’s opening drive. Members of the team’s medical staff examined his left arm and shoulder as he sat on a table behind the Redskins’ bench. He twice returned to the game but failed to finish it.

He underwent offseason surgery for a partially torn left pectoral muscle suffered in last season’s finale. Orakpo aggravated the injury in the second preseason game in Chicago and missed the final two exhibition games.

Yet he was in the lineup for the Redskins’ victory at New Orleans to open the regular season.

Shanahan said this injury was to a different part of the same pectoral muscle.

Shanahan said that fourth-year pro Rob Jackson and fifth-year pro Chris Wilson will be given practice-field looks at Orakpo’s outside linebacker spot and a starter will be chosen later in the week.

“It’s a big opportunity, not only for myself but for any backup,” Jackson said Monday. “You’re a backup in a position waiting for that day or that game that you actually start a game. We’ll see how the week goes and see what decisions they make.”

The Redskins re-signed Carriker as a free agent in March after he started 15 of 16 games and had 51 / 2 sacks last season. Jarvis Jenkins, a second-year pro who missed all of his rookie season because of a torn anterior cruciate ligament in his right knee, takes over as the starter at left end.

“Last year when I tore my ACL, everybody had to step up and play a role,” Jenkins said. “We brace for times like this. That’s why everybody gets reps. That’s why everybody watches film. When one guy goes down, like Coach Shanahan says, we shouldn’t have a dropoff. That’s why they pay us to do this job. It’s a business. We’ve got to come in this week and just work.”

Meriweather hurt his left knee in the second preseason game and missed the final two exhibition games. He resumed practicing fully before the season but, six days before the opener, landed awkwardly on the knee and suffered sprained medial collateral and posterior cruciate ligaments. The Redskins said at the time that Meriweather would be sidelined for two to four weeks.

Meriweather said Monday that he will try to play this week but is unsure if he will be able to do so. He said his knee has improved since last week but he didn’t know when he will be cleared to participate fully in practices again.

“I have no idea,” Meriweather said. “If it was up to me, I would have been [practicing fully] last week.”

Shanahan said the Redskins will re-evaluate Meriweather’s status Wednesday.

The Redskins have yielded 56 points on defense in two games, plus seven more on a blocked punt returned for a touchdown in New Orleans. Dating from last season, the Redskins have surrendered 30 or more points in four straight and six of their last seven games. The Rams piled up 452 yards on offense Sunday.

“The first game, I think, was kind of a little misleading,” linebacker Ryan Kerrigan said Monday. “We did allow 25 points. But that’s one of the best offenses in the league. We gave up a lot of yards but we were able to come through in the red zone. We did that in the early stages [Sunday]. But then in the back half of the game the yards just started piling up and they were able to get it in the end zone, which we can’t have happen.”