Manchester United's signing of Romelu Lukaku has come at "the perfect time", according to the club's former striker Ruud van Nistelrooy.

The Belgium international completed a move to United this month for a reported fee of £75million and has already netted twice in three pre-season outings, including in the 2-0 win over Manchester City in Houston this week.

Van Nistelrooy scored 150 goals in just 219 games for the Red Devils and became a favourite of the Old Trafford faithful before leaving for Real Madrid in 2006.

And the former Netherlands star expects Lukaku to achieve a similar status among the supporters if he makes the most of his move from Everton.

"I actually remember playing against Romelu Lukaku. I was at Hamburg, he was at Anderlecht, and it was in the Europa League," Van Nistelrooy told United's official website.

"I was so impressed with his fitness and physical ability, as well as his touch. His will to succeed was incredible, he never gave in and always kept fighting. Even from a young age, I was impressed by him.

"He's unbelievably strong and, with the pace he has, he often puts away the chances he gets. I think he's one of the true number nines, like Harry Kane at Tottenham – they're strong centre-forwards who are also a reference point during the build-up play. Romelu is strong on the ball but also when making runs and finishing chances.

"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."

Lukaku was sold to Everton by Jose Mourinho when he was Chelsea manager in 2014, but the 24-year-old said that working with the Portuguese again was one of the reasons behind his decision to join United.

Van Nistelrooy believes Lukaku will thrive under the ex-Inter and Real Madrid boss, adding: "I don't think he could be playing for a better manager than Jose Mourinho.

"He will help and guide Lukaku through this stage in his career and, if he has any difficulty, Jose has the experience and advice to get players back on track. I think that combination will prove a very successful one."