Williams, Atlanta's primary nickel back and a ninth-year veteran, was injured in the regular season finale win over Carolina. If Williams can't play, Christopher Owens will take his place.
Owens ended last season as a left-side starter for Atlanta, but lost the job to Brent Grimes in training camp. He was the primary nickel back until Williams replaced him before a home victory over Tampa Bay on Nov. 7.
Williams underwent reconstructive surgery on his right knee in October 2009 and missed the rest of the season. Owens took his starting spot.
The Falcons (13-3) are the NFC's top seed. Green Bay (11-6) advanced with a wild-card win last week at Philadelphia.
After practice Friday, Atlanta listed receiver Roddy White (knee), defensive end John Abraham (groin), defensive tackle Jonathan Babineaux (shoulder), middle linebacker Curtis Lofton (limited) and safety Thomas DeCoud (ankle) as questionable.
Green Bay listed linebacker Clay Matthews (shin), cornerback Charles Woodson (toe) receiver Donald Driver (knee), offensive tackles Chad Clifton (knees) and Bryan Bulaga (shoulder), linebacker Diyral Briggs (ankle) and defensive ends Cullen Jenkins (calf) and Ryan Pickett (shin) as probable.
Linebacker Frank Zombo is out with a knee injury. Safety Atari Bigby (groin), running back Korey Hall (knee) and center Jason Spitz (calf) are questionable.