Moss, who was downgraded from questionable to doubtful Friday, was hurt Oct. 22 at Indianapolis.
"You're going to miss Santana," Coach Joe Gibbs said on Washington's Web site. "We all know that. We have to have other guys step up. It's why we have the guys we do at that position. Hopefully, that will happen."
Moss, in his sixth season out of Miami (Fla.), has more yards receiving (435) than the other four wide-outs on the roster combined (397) this season.
"I feel pretty good, but at the same time, you see how I'm dressed," said Moss, who wore sweat clothes to Friday's practice.
Washington carries a three-game losing streak into Sunday's game.