Washington Redskins left tackle Trent Williams won't play Sunday against the Dallas Cowboys due to a right knee injury, a source told ESPN's Dan Graziano, further depleting the offensive line. Center Spencer Long was ruled out Friday because of quad and knee tendonitis.

Williams' absence isn't a huge surprise, considering that earlier in the week he and coach Jay Gruden said there was a chance that he would have to sit out a game or two. But it's still a blow to a team that has two other starting linemen questionable: right guard Brandon Scherff (knee) and right tackle Morgan Moses (ankles).

"We have to do right by Trent," Gruden said earlier in the week.

Williams said his knee will eventually need surgery, but he's trying to see how long he can play with the pain. He said earlier in the week that it prevented him from making certain blocks in Monday's loss to the Eagles. He struggled on some backside blocks when needing to react to a defender's movement. He had a harder time holding his blocks when trying to drive his man.

After the Eagles' game, Williams said "probably so" when asked if it would be better to take a week or two off.

"I'm just trying to push through," he said.

That's what he has done in previous years, but he admitted this injury has been among the worst he has endured. But even at less than full strength, Williams was able to handle his protection duties and get out on screens. The Redskins' screen game, especially to running back Chris Thompson, has been a crucial part of the offense. It would take a big hit if both Williams and Scherff can't play. Their ability to block in space has been crucial.

The problem with Williams missing is that the Redskins' top backup tackle, Ty Nsekhe, will miss his fourth game with a core muscle injury. That means T. J. Clemmings, who started two seasons at both right and left tackle in Minnesota, will take over. Rookie Chase Roullier will start at center.

If Scherff can't play, Tyler Catalina would start at right guard. That isn't an ideal way to face a Cowboys rush that, while devoid of a top speed rusher, has recorded sacks on 9.5 percent of dropbacks -- seventh best in the NFL, according to ESPN Stats & Information.