Jason Campbell was carted off the field of Thursday night's game against Chicago with a dislocated left kneecap.
Campbell's status will be updated on Friday. He is scheduled for an MRI to further evaluate the extent f the injury.
"I think the good news is that it's not a ligament injury," head coach Joe Gibbs said. "They think it's a kneecap-type issue. We will have to wait. I'm hesitant to say anything more than that."
Campbell was replaced by 13-year veteran Todd Collins.
The injury occurred late in the second quarter. Campbell dropped back to pass and threw across his body to Ladell Betts for a 7-yard gain. Just as Campbell got rid of the ball, defensive end Mark Anderson dragged him down.
Campbell fell awkwardly and his left knee buckled under the weight of the 255-pound Anderson.
On the ground, Campbell immediately grabbed his knee and took off his helmet. He was in obvious pain.
Athletic trainers tended to Campbell and put the kneecap back in place. As Campbell was carted of the field with a black wrap covering the injured knee, he pumped his fist into the air twice to acknowledge fans.
Campbell finished the game completing 10-of-16 passes for 100 yards.
Collins turned in a solid performance in relief, completing 15-of-20 passes for 224 yards and two touchdowns in the Redskins' 24-16 win.
A couple plays before the knee injury, Campbell had injured his right elbow but he was able to return to the game.
Campbell had scrambled left for two yards, but as he veered out of bounds, cornerback Brandon McGowan nicked him on the elbow with his helmet.
Trainers tended to Campbell on the field. Later, Campbell tested the elbow on the sidelines with practice throws, and he came back into the game on the Redskins' next offensive series.