The Old Trafford legend has been impressed by the fitness and physical ability of the former Chelsea and Everton hitman, who is "a true No.9"
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 £75 million 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.