Williams went down in his side's pre-season clash with the San Francisco 49ers after taking a low hit from offensive lineman Joe Looney.
A statement released by Frazier said: "Williams suffered a hyperextension injury to his right knee in last night's football game.
"An MRI exam today revealed a significant bone contusion as well as a posterior capsular strain.
"Kevin was fortunate in that there was no injury to any of his ligaments."
Minnesota face the Detroit Lions in their regular season opener on September 8.