The Redskins reeling defense suffered a devastating blow Monday when it was announced that star linebacker Brian Orakpo will miss the remainder of the season with a torn left pectoral muscle.Orakpo, two-time pro bowl selection, suffered the injury early in Sundays 31-28 defeat in St. Louis while wrapping up Rams quarterback Sam Bradford for his first sack of the season. Its the same pectoral Orakpo tore in the 2011 regular season finale and aggravated in the preseason. This tear, though, in a different spot.Rak tore his pec in a little different spot on the right side, Shanahan said. It will be about four-month recovery time. So hell be gone for the season as well.Moments earlier, Shanahan confirmed what most had suspected: Defensive end Adam Carriker will also miss the remainder of the season. He tore a ligament between the quadriceps and knee, Shanahan said.The loss of Orakpo, however, was a stunner.After getting hurt early in the game, the 26-year-old returned to the game twice, including early in the second half. Both times, however, he was forced to leave the field again.According to the MRI, its a completely different area than the initial tear, Shanahan said, asked if the new injury was related to the prior one.Shanahan said Orakpo and Carriker will have surgery this week. Shanahan said Orakpo will miss four months, while Carriker will be sidelined five.Neither player was available to speak to reporters Monday.Orakpo is expected to be replaced by Rob Jackson, who said earlier in the day that he was preparing as though he would be the starter against Cincinnati. Orakpo's absence figures to result in Chris Wilson will receiving additional playing time, too. Shanahan hinted that Jackson and Wilson could compete to be Orakpo's full-time replacement.They both have to step up and play at a very high level because we all know what Rak has meant to our defense and how well hes played, Shanahan said of Jackson and Wilson.Orakpo has averaged 9.5 sacks per game during his first three seasons in the NFL. And after an offseason spent rehabbing and working on technique, he was hoping to have a breakout year."He's a guy who can do it all," Shanahan said. "He can cover, he rush, he can play the run, he's very physical, very smart, a team player. All the things you look for in a Pro Bowl player. Obviously, we're going to miss him."