"I am very happy to join Manchester United," said the youngster, who will miss the club's pre-season tour of the Far East because of an injury.
"This is a big opportunity for me to play at such a great club. I am very excited to be here and I look forward to proving what I can do."
Manchester United have already signed 23-year-old Ecuador winger Antonio Valencia this summer as Ferguson tries to replace Cristiano Ronaldo, the world player of the year, who has joined Real Madrid for a world record £80m.
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