Backup linebacker Nick Barnett will miss the final game of the season after tearing the medial collateral ligament in his left knee, Coach Mike Shanahan said. Meanwhile, starting right outside linebacker Brian Orakpo is day-to-day with a groin strain. Barnett suffered the injury while playing on Washington’s kick-return unit early in the first quarter. He left the game with what at the time was called a sprain, but the team learned the full extent of the injury on Monday. Barnett had arthroscopic knee surgery during the offseason, and then signed with Washington on a one-year deal early in training camp. An 11-year veteran, Barnett had started every season of his career (eight with Green Bay and two with Buffalo) until this season, when he served as London Fletcher’s backup and contributed on special teams. Shanahan said that Barnett isn’t expected to require surgery for the MCL to heal. Rookie inside linebacker Will Compton, who has spent the entire season on the team’s practice squad, will receive the promotion to the 53-man roster. Orakpo, Washington’s top pass-rusher, suffered a right groin strain early in the fourth quarter of Washington’s loss to Dallas. The Redskins held a 23-14 lead at that point, but Dallas came back to win 24-23, and the defense struggled to pressure quarterback Tony Romo down the stretch of the game.