The 23 year old left back did agree to join Southampton earlier, but an argument between the player and his old club put an end to the Saints interest.
United moved quickly for Buttner once interest from Southampton had cooled, a move that came as a shock to fans who all thought United were after Everton defender Leighton Baines.
Buttner comes from the The Ajax academy product, he was not capped by Netherlands at youth level beyond Under-20 and has not played for the senior side.