Paul suffered the concussion when he caught a pass and was hit by multiple defenders.
The 25-year-old had been filling in for starter Jordan Reed, who has missed the last three weeks with a hamstring strain.
Paul will have to go through the league's concussion protocol before returning to the field. In four games this season, he caught 21 passes for 313 yards and a touchdown.
Williams could play in the Redskins' next game, Monday Oct. 6 against the Seattle Seahawks.
Niles Paul is going through concussion protocol. No timetable, obviously.— Tarik El-Bashir (@TarikCSN) September 26, 2014