Linebacker LaVar Arrington sat out practice on Wednesday to rest a thigh injury and he is officially listed as questionable for Sunday's game against the Arizona Cardinals.

Arrington aggravated the thigh injury in the first half of Sunday's game against the Rams. He left the game, but returned to finish out the second half.

If Arrington is unable to play, veteran Warrick Holdman would likely start in his place. Holdman started the Redskins' first seven games this season before being replaced by Arrington. Holdman has 27 tackles this season.

In recent weeks, Arrington has been particularly effective as a run defender, frequently bursting into the backfield to tackle running backs for losses. On the first play of last Sunday's 24-9 win over the St. Louis Rams, Arrington tackled tight end Cameron Cleeland for a 7-yard loss on a swing pass.

For the season, Arrington has 46 tackles (39 solo) in six starts.

Also on defense, tackles Joe Salave'a (foot injury) and Cedric Killings (groin) are listed as questionable on the team's injury report. Neither played in last Sunday's game against St. Louis.

Meantime, wide receiver Santana Moss suffered a mild hamstring injury during Wednesday's practice. He is listed as probable for the Arizona game.

Wide receiver James Thrash, who has missed the last two games with a hamstring injury, participated in some drills during Wednesday's practice but remains questionable.

"James took some light work, but I think we're still a ways off," head coach Joe Gibbs said. "It's probably something we'll talk about later in the week."

Running back Ladell Betts returned to practice on Wednesday, the first time the fourth-year running back has worked in three weeks. Betts is not on the team's injury report, signaling that he should be available for Sunday.