The 30-year-old played through the pain barrier during the 2011 season, which has led him to take caution with injuries after his performances suffered as a result.
Williams told ESPNWisconsin.com: "I'm not concerned much at all. Obviously at this point, I'm just sitting and resting it.
"According to the doctors, it's not serious. That's about all we can do at this point. It's just one of those things that needs rest.
"You can never put a timetable on injuries. You don't want to come back too fast and have a setback. You'd rather wait around until you know you can go full speed."
Green Bay open their pre-season campaign against the Arizona Cardinals.