With the new contract, the talented 19-year-old will stay with the club until 2010.
Rossi told MUTV: “It’s great of course. Just staying with United for another two years is incredible. This is one of the best teams in the world and it’s where all the players want to be.
“I feel blessed with the opportunity to stay. I’ve played two years with the reserves and we won everything, all the trophies we could. This year we want to step it up and keep winning.”