The 18-year-old has put England international’s Wes Brown and Gary Neville out of the team at Old Trafford.
Fergie said: “Gary and Wes are England’s best right full-backs.
“But they have a little problem because this young boy Rafael has really taken off.”
He added: “All the players, Gary included, are so supportive of him. They think he is fantastic.
“It is rare for someone to come through like he has done.
“When Gary did it, he had help. He was among six or seven young players all together, like a band of brothers.
“This lad doesn’t speak the language that well but he understands the football very well.”