Williams sat out practice Friday for the second time in the last three days. He was limited in Thursday's workout.
William ranks fifth in the NFL with 768 rushing yards, including 307 in the past two games.
Fellow running back Jonathan Stewart (Achilles' tendon), wide receiver Muhsin Muhammad (knee), tight end Dante Rosario (knee) and fullback Tony Fiammetta (concussion) are all listed as questionable for Sunday's game. However, all four players practiced Friday.
Fullback Brad Hoover and safety Charles Godfrey are doubtful and haven't practiced all week because of ankle injuries.
Defensive end Julius Peppers is probable with a hand injury.
Copyright 2009 by The Associated Press