The Bucs also announced Wednesday that guard Michael Shumard has been claimed off waivers from the Denver Broncos. Offensive tackle Robert Okeafor was released.
Williams was the fifth overall pick in the 2005 NFL draft and was the league's offensive rookie of the year that season. He has rushed for 3,240 yards and 18 touchdowns in five years, despite missing most of two seasons with career-threatening knee injuries.
After being sidelined for most of 2007 and 2008, Williams played all 16 games and led the Bucs with 823 rushing yards and four touchdowns last season.