The former Vitesse Arnhem defender has already made an impact for the Red Devils by scoring on his debut against Wigan in September.
Buttner - a £3.9million signing - is now putting pressure on 31-year-old Patrice Evra for a regular start at left-back, although the Frenchman has been first choice since he signed in 2006.
Buttner has impressed everybody at the club and even the Dutchman has been surprised by how much game time he has been handed by the boss.
He said: "I have played more than I had expected. New players tend to be gradually brought into the team at United.
"It is great to be on the training ground with such fantastic players everyday. It really improves you as a player."
Buttner has also hailed the great form of his former side in the Eredivise.
Fred Rutten's side currently sit third in the table and are just five points off leaders PSV Eindhoven after the opening 12 games.
"It doesn't surprise me (Vitesse's form) because last year I noticed there was a lot of quality in the team. It is a solid side with so much individual quality.
"I am not going to say that Vitesse will be champions, but they will certainly be up there until the end. I watch every game on television and I think the way they're performing at the moment is fantastic."