The 23-year-old became the club’s fourth summer after signing a five year deal following the earlier arrivals of Robin van Persie, Shinji Kagawa and Nick Powell.
Fergie believes he will be a great acquisition: “Alexander is one of the best young left backs in Europe and we’re delighted to sign him. He’s someone we’ve been watching for a while now. He gives us some really exciting options in that position,” the United boss said.
Meanwhile, the defender himself cannot wait to make his United debut.
He said: “It’s a team I have admired for many years now and I can’t wait to join my team-mates and play my part in helping the club be successful.”