He will be placed on injured reserve, ending his season.
The versatile second-round draft pick from Virginia Tech will need surgery to repair the damage and won't be back until next year.
Williams' leg got twisted underneath him on a tackle.
The Cardinals are going with Beanie Wells, and they'll need another running back after trading Tim Hightower to the Washington Redskins.
This represents a major blow to the Cardinals' offense because of Williams' multi-dimensional skills.
The Cardinals will likely need to add another back, but do have LaRod Stephens-Howling and Alfonso Smith on the roster.