Williams hurt his knee in last week's loss to Cincinnati and did not practice Wednesday or Thursday. He was limited in Friday's session.
Garcon is dealing with a foot injury that has forced him to miss the last two games.
Brandon Banks, who is the team's kick returner, has a hip injury.
The Redskins have ruled out cornerback Cedric Griffin because of a hamstring injury.
Meanwhile, safety Brandon Meriweather is listed as probable after missing the first three games with a sprained left knee.