The Vitesse Arnhem fullback trained with United this morning after undergoing a medical yesterday.
Dad Christian is with his son in Manchester and they were given a tour of Old Trafford and the club's Carrington training complex.
"It was great to see and experience. We have not been to the match against Everton, because we just came from the stadium. These are busy days," smiled Christian.
Buttner's presentation as a United player is slated for Friday.