Kevin Williams not practicing on Monday

There was no sign of Kevin Williams in the portion of Vikings practice open to reporters on Monday, and if the defensive tackle isn't able to turn things around early this week, he could have a tough time returning from a knee injury in time for the team's season-opener in Detroit on Sunday.

Williams hyperextended his right knee on Aug. 25 when 49ers offensive lineman Joe Looney blocked him low, and while coach Leslie Frazier said the Vikings were shooting to have Williams available for Week 1, it seemed questionable whether the 32-year-old would be able to return that quickly. If he's unable to go, the Vikings would have to shift more work toward rookie Sharrif Floyd, who was practicing Monday after recovering from his own knee injury.

Floyd had minor surgery to relieve discomfort in his left knee from a low block in the Vikings' first preseason game. He is expected to play this week, but the Vikings had hoped to use him in a rotation with Williams. Unless Williams makes progress throughout the week, that plan could change.

Williams was the only player missing from Vikings practice on Monday morning.