Manchester United legend Ruud van Nistelrooy is convinced that Romelu Lukaku will be a huge asset for manager Jose Mourinho next season.
The Belgium international moved to Old Trafford for Everton and has already scored his first goal for the club.
"He's proven himself at Everton," the Dutchman told the club's official website.
"His challenge now is to make another step up and to prove himself at his new club as well. It's different playing at United to playing at Everton, so it will be a mental step, too.
"The pressure is different, so if he's capable of dealing with that, I can't see any problems. I also think having better players around him will help and I think he'll fit in really well.
"I expect he'll start hitting his peak now. From the club's point of view, it's the perfect time to sign him.
"Over the next six, seven or eight years, United will hopefully have a great centre-forward in Romelu Lukaku."
