Stoops did not disclose a reason for the dismissal.
Williams rushed for 553 yards and seven touchdowns this season, a year after leading the team with 946 rushing yards and 11 touchdowns in 2012.
The No. 18 Sooners, however, didn't miss him much at Kansas State. Brennan Clay shouldered the rushing load well with 200 yards and two touchdowns on 31 carries in Oklahoma's 41-31 win over the Wildcats.
The Sooners (9-2, 6-2 Big 12) are off this weekend and close the regular season Dec. 7 at seventh-ranked Oklahoma State (10-1, 7-1).