Reserve running back Tyrell Sutton is also doubtful after sitting out Friday with a calf injury.
Williams was injured in the first quarter of last Sunday's win over Minnesota and didn't return. Jonathan Stewart replaced him and rushed for 109 yards and a touchdown.
Stewart is questionable with a sore left Achilles tendon, but practiced Friday.
Quarterback Matt Moore (shoulder) and cornerback Richard Marshall (ankle) are also questionable. Both practiced Friday in a workout that took place on the Bank of America Stadium concourse because of heavy rain.