The speedy linebacker, though, says he will play against the New England Patriots in Super Bowl XLVI.
"It's nothing serious," Williams said. "I'll be there. I'll be ready for the game."
Williams was one of four Giants who did not practice Friday. Wide receiver Hakeem Nicks sat out practice with what he says is a sprained AC joint in his shoulder. He also says he will play against the Patriots.
Cornerback Corey Webster rested his hamstring injury and cornerback Will Blackmon sat with a knee injury. Coach Tom Coughlin has said the team is being careful with all injuries and making sure everybody will be ready for the Super Bowl.
Running back Ahmad Bradshaw (foot), center David Baas (abdomen/neck) and linebacker Chase Blackburn (calf) went through a limited practice after sitting out Thursday. All three say they will play against the Patriots. Defensive end Osi Umenyiora (ankle/knee) also went through a limited practice as part of his routine.
Williams did not know how he injured his foot in the NFC Championship Game against the 49ers, but he said his foot was sore and that doctors told him he had a foot sprain and to rest. He underwent an MRI that revealed nothing more than a sprain, and he says he will practice next Wednesday in Indianapolis.
"It's nothing too bad, I'll be ready," he said. "It ain't no turning back, I'll be there."
Nicks said he landed on top of his AC joint and that his shoulder is still sore but doing better. He briefly left the 20-17 overtime win in San Francisco before finishing the game. He has repeatedly said he will not miss the Super Bowl.
"I expect to be a full go by next week," Nicks said. "Just using next couple of days to rehab it. It was painful. I landed right on an AC joint that I have injured a few times this season. Went in and got it taken care of and by halftime I was cool."
Ohm Youngmisuk covers the Giants for ESPNNewYork.com. Information from ESPNNewYork.com's Ian Begley contributed to this report.