Williams was caught from behind with a chop block by San Francisco guard Joe Looney and was unable to continue as he limped off the field.
The 33-year-old, who is set undergo an MRI scan later today, insisted that he felt fine after the match but was unhappy with the tackle that caused the injury.
"I feel all right. Don't really know what's wrong, but I think I'm fine. I was just upset that I'm getting cut like that 11 years in from a guy I don't even know who the guy is," Williams told reporters after the match.
"Between the pain and the fact that no-one was looking it was terrible."
Vikings coach Leslie Frazier is thought to be considering sending a video of the play to the league office in order for Looney to be disciplined, having not been penalised when the offence initially took place.