The injury will not require surgery and will be evaluated weekly by the Duke medical staff.
"We are confident that he will make a full recovery," coach Mike Krzyzewski said in a statement. "Mason is going to be a very good player for us and we look forward to him getting healthy and returning to the court."
Plumlee is a McDonald's All-American who averaged 12 points, eight rebounds, three assists and three blocked shots in exhibition wins over Pfeiffer and Findlay.
Duke opens their regular season Friday night at 7 p.m. against UNC Greensboro.