Rookie Keenan Robinson suffered a pectoral muscle injury on Thursday. (Matt Strasen/Associated Press)

Washington Redskins rookie inside linebacker Keenan Robinson was undergoing tests on Friday to determine if he had suffered a torn pectoral muscle, and the fear is that Robinson could be lost for the season.

Drafted in the fourth round out of Texas, Robinson has played primarily on special teams this season, but he also has been used on certain pass-rushing situations and to spell 15-year veteran London Fletcher.

“I think he’ll be an every-down player for years to come,” Coach Mike Shanahan said in a teleconference on Friday. “The more experience he gets, obviously, the better he’s going
to be. He’s got speed, he’s got quickness, he’s not afraid to hit [and[ extremely bright — that’s a big upside.”

Robinson on Thursday played 19 defensive snaps and 21 special teams snaps in Washington’s 38-31 victory over the Dallas Cowboys on Thanksgiving night. He appeared to suffer the injury while trying to tackle tight end Jason Witten late in the game.

“Right now, it doesn’t look good,” Shanahan continued.

Fellow linebacker Brian Orakpo suffered a torn pectoral muscle in the 2011 season finale and had surgery to repair it in January, but then suffered the same injury in Week 2 of this season and was lost for the season. Orakpo had surgery to repair the muscle again, and is expected to return to full strength next year.

Shanahan said that Robinson has impressed him in the limited action he has seen this season. The coach believes that the 6-foot-3, 238-pound Robinson has a bright future with the team.

Shanahan said he wasn’t sure Fletcher would be able to start Thursday’s game and said the veteran linebacker should benefit from a weekend of rest before the Redskins began preparations for their Dec. 3 game against the New York Giants. Fletcher played in the Redskins’ victory over the Cowboys, extending his consecutive-games streak to 235, but he was unable to finish the game after aggravating his sprained left ankle.

“His ankle is quite sore,” Shanahan said said. “He needs the extra days of rest. Knowing what type of competitor he is and how sore he was going into this last game, I really didn’t think there was a chance for him to play in the back of my mind. When he was able to play in that game — the type of desire he had to actually play the whole game or close to it, looking at him, early in the week, I’m never counting him out again.”