Buttner was handed a start for the FA Cup draw at West Ham United.
"We took him for the future and to succeed Patrice Evra," said Ferguson. "What we wanted was an attack-minded left back and we see this in him. He trains very well, has a house and is completely settled here in England.
"You come from another culture, to another country at a big club. That's a big change.
"So it helps if someone like Robin (van Persie) has extensive experience in England. Of course they talk a lot with each other, that's understandable."