The Republic of Ireland midfielder, now 24, made his senior Reds debut a day after his 18th birthday, in a League Cup third-round tie against Barnet in October 2005.
Gibson went on to play 60 times for United, netting 10 goals during his Old Trafford career. Those strikes included goals against German opposition in Champions League quarter-final (Bayern Munich, 2010) and semi-final ties (Schalke, 2011).
A foot injury sustained last summer during pre-season kept Gibson out of first-team action until the Reds’ Carling Cup fifth round fixture against Crystal Palace on 30 November. His only other appearance in 2011/12 came on Boxing Day when Wigan Athletic visited Old Trafford.
Gibson vacates the number 28 shirt at Old Trafford and will wear the number four for his new club.
Everybody at Manchester United wishes Gibson all the best for the future.