The 19-year-old was charged by police earlier this month after his car collided with a van while he was drink-driving in Manchester.
Tunnicliffe, who could have his ban reduced by four months if he attends a rehabilitation course, was also given an £800 fine.
Presiding magistrate District Judge Richardson of Bury Magistrates' Court said: "You are a well-paid athlete and the fine reflects that. It is a reflection of your income."
Tunnicliffe made his senior debut for the Red Devils during a League Cup match against Newcastle United last month.