Linebacker Brian Orakpo injured his pectoral muscle in the Redskins' Week 2 loss to St. Louis.
Two-time Pro Bowl linebacker Orakpo tore the pectoral muscle near his left shoulder, and defensive end Carriker tore the quad tendon in his right knee in the first quarter of Sunday's 31-28 loss to the St. Louis Rams.
The injuries rob two players from a team that has allowed 63 points and more than 800 yards in its first two games, tempering the early promise by Redskins (1-1) have shown with rookie quarterback Griffin.
"It's an opportunity for somebody else now," linebacker London Fletcher said. "We're a no-excuse football team."
Orakpo had surgery on the same shoulder after a suffering tear in the final game of last season, then damaged some scar tissue in the shoulder during a preseason game last month.
Coach Mike Shanahan said the latest tear is in a different part of the muscle. Orakpo will have surgery and require four months of recovery time.
Orakpo, a first-round draft pick in 2009, had at least 8½ sacks in each of his first three NFL seasons. He was injured Sunday while making his first -- and only -- sack of this season. He returned to the game twice but was unable to keep playing.
"He's obviously everything you look for in a Pro Bowl player," Shanahan said. "And we'll miss him."
Graziano: Doesn't Get Much Worse
Monday's news was a crushing blow for the Redskins, for whom Brian Orakpo and Adam Carriker are critical pieces in a defensive front seven that was the strength of their team, ESPN.com's Dan Graziano writes. Blog
Shanahan said Rob Jackson and Chris Wilson, a pair of career backups without an NFL start between them, will compete to take Orakpo's outside linebacker spot.
Carriker was hurt on the Rams' second offensive play and did not return. The fifth-year veteran, who had 5½ sacks a year ago, will require five months of rehabilitation after his surgery.
He will be replaced by Jarvis Jenkins, a 2011 second-round pick who missed his entire rookie season with a knee injury.
"A real big opportunity," Jenkins said. "Coming off the knee injury, I get a chance to prove I'm a hard worker and just make plays."
Two other defensive starters also are nursing injuries. Cornerback Josh Wilson left Sunday's game with a concussion and will be reevaluated Wednesday, and safety Brandon Meriweather hopes to play this week against the Cincinnati Bengals after missing the first two games with sprained ligaments in his left knee.