The 23-year-old was wanted by the likes of Southampton, Fulham and Queens Park Rangers earlier this summer - but now United have made their move and are ready to seal a five million euros deal.
Buttner has already declared the move a dream, and as he left Schipol Airport in Amsterdam for Manchester, he admits things were still sinking in.
"If a week ago, you told me that together with Robin van Persie I would be playing at Manchester United, I would have driven you straight to the mad house," he said.
"One month ago Manchester United sent an email expressing their interest, but in the last four days it became concrete.
"I have not spoken yet with Sir Alex Ferguson, but if all goes well that will happen."
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Buttner has been in dispute with Vitesse Arnhem over his future and has been training away from the first-team squad.
"With not being allowed to train with the first team and the arbitration case against Vitesse, this was not a nice time so I see this as a reward," he added.