Wayne Rooney believes that for Romelu Lukaku to succeed at Manchester United, he will need to learn how to deal with the immense pressure of playing for the club.
The former Red Devils star, who completed his return to boyhood club Everton on Sunday, believes that while Lukaku has all the technical ability to slot in comfortably at Old Trafford, he will need to focus on his mental stability if he is to achieve true greatness.
"Playing for Manchester United is a test of character," Rooney, who marked his return to the Toffees by scoring a long-range screamer against Gor Mahia on Thursday, told reporters.
"You've got to be strong enough mentally to accept the challenge," the 31-year old continued. "United are a football club that demands success. Romelu has to be strong enough to take up that challenge.
"If he does that then, with the ability he has got, then he will be a success. If he worries about things then it will be more difficult.
"Hopefully, Romelu has got people there who will give him the right guidance and get the best out of him," he added.
The former Red Devils captain continued by noting the pressure that new Manchester United players face, saying that the club's phenomenal success under former manager Sir Alex Furgeson casts a long shadow over the club.
"There are standards that you have to keep when you are at Manchester United. That came from Sir Alex when I went to United and it was passed down through the likes of Giggsy [Ryan Giggs], Gary Neville and Scholesy [Paul Scholes].
"Over the last few years, it was down to me and Michael Carrick to keep the new players maintaining those standards.
"That has been more difficult over the last few years, with some of the players who joined the club. There are traditions at United that have to be maintained.
"It has become harder, but that's not my problem anymore. I'm just ecstatic to be back at Everton," he added.