It is likely to keep him out of action for a fortnight, almost certainly ruling him out of the opening day clash on August 7.
Lee Ridley will step into the side in his absence, starting with tonight's Lincolnshire Cup game against Grimsby Town at Blundell Park.
United could play trialist Bill Sharp in the match, after asking permission from Lincolnshire FA to include the Sheffield United youngster - who scored against Rangers U21 on Tuesday night - in the starting lineup.