Manchester United hero Ruud van Nistelrooy is impressed by new signing Romelu Lukaku.

Although Van Nistelrooy admits it will take a mental adjustment for United's new striker after previously shining at Everton, he believes that Lukaku can build on the form that saw him top 25 goals in each of the last two seasons.

Van Nistelrooy told ManUtd.com: "Well, he's proven himself at Everton. 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."