Williams sat out practice Friday for the second time in three days. He was limited in Thursday's workout.
William ranks fifth in the NFL with 768 yards rushing, including 307 in the past two games.
Fellow running back Jonathan Stewart (Achilles' tendon), receiver Muhsin Muhammad (knee), tight end Dante Rosario (knee) and fullback Tony Fiammetta (concussion) are all listed as questionable for Sunday's game. But all four players practiced Friday.
Defensive end Julius Peppers is probable with a hand injury.