The young right-back played the full 90 minutes of United's friendly win at Peterborough and did enough to suggest a competitive debut may not be too far away. His brother Fabio also impressed, at left-back, after coming on for Patrice Evra at half-time.
Ferguson told MUTV, "The young players were fantastic and young Rafael the right-back was a sensation for me.
"I thought it was a real eye opener for us. He hadn't played for a year but he's played a full 90 minutes today. His brother Fabio has played 45 minutes and he's also done well so we're really pleased by their contribution."
He added: "You know what football's like. Sometimes it turns up some star, some little nugget maybe. On the evidence of tonight I think we have got a good player here."