The 22-year-old has become a key member of Ferguson's squad this season following several spells on the sidelines with a succession of injuries.
Discussing the defender's rise into the first team, Ferguson has likened Rafael to former United full-back Gary Neville.
"We invest in young players and we get repaid at some point," said Ferguson. "Rafa can develop the kind of career Gary Neville had. Gary was not the finished article when he came into the team but he got better and better and became a fantastic full-back, probably the best the club has ever had.
"Rafael is definitely a more naturally talented right-back because Gary came to us as a centre-back."
Rafael has made 103 appearances for the Red Devils in all competitions.