Sean Taylor will miss at least two weeks due to a sprained knee he suffered in Sunday's game against the Philadelphia Eagles.
After two weeks, coaches and athletic trainers will re-evaluate Taylor's injury to determine his status for the final stretch of games.
Taylor was at Redskins Park on Monday, walking gingerly on his injured knee. He underwent an MRI on Monday morning and it was determined he suffered a Grade 2 sprain of his MCL.
"I would say he will be out for a little while," head coach Joe Gibbs said. "How long? I'm careful to say with these guys because physically they aren't like the rest of us. We just need to take it day by day, but I would assume he will be out for a little bit."
With Taylor sidelined, the Redskins' defense will certainly be challenged this Sunday when they take on the Dallas Cowboys at Texas Stadium
The Cowboys have the NFL's third-ranked offense, averaging nearly 400 yards per game, and league's second-ranked passing offense.
Pierson Prioleau is expected to take Taylor's place at free safety, but assistant head coach-defense Gregg Williams could use several defenders and defensive packages to make up for Taylor's absence.
Said Gibbs: "What happens in the NFL down the stretch is that guys have to step up. There are going to be some guys missing this week with injuries, so other guys are going to have to step up.
"We need to keep playing physical and keep working hard in practice like we are doing."
The Redskins' defense received some good news on Marcus Washington, who sat out the Eagles game due to a hamstring injury.
Washington is expected to participate in practice this week and he should be available to play against the Dallas Cowboys.
-- UPDATE ON THRASH
James Thrash suffered a high ankle sprain in Sunday's game against the Eagles. He was at Redskins Park on Monday walking on crutches.
His status for the Dallas game will be determined later this week, but team officials were not optimistic he would be available.
"It would depend on James," Joe Gibbs said. "I want to see him during the week. But I was told it was mild."
Gibbs praised Thrash for his performance on Sunday. Playing against his former team, Thrash had five catches for 85 yards and two touchdowns. He also had a special teams tackle.
"He means a lot to us in a lot of different places," Gibbs said. "I think James had caught three passes all season up until his opportunity [against the Eagles], so I can't brag on him enough.
"That's an example of what can happen and what we are going to need to happen down the stretch here for us to play well."
-- FOR MOSS, A TIME TO HEEL
Joe Gibbs revealed that Santana Moss underwent an MRI on his injured heel on Monday. The results proved what team officials thought all along: his heel is bruised sore.
Moss sat out Sunday's game against the Eagles as a result of the injury.
Moss is expected to increase his running as the team begins practice on Wednesday. His status for the Dallas game will be determined later this week.