Wayne Rooney has warned Romelu Lukaku he must show mental strength if he wants to be a success at Manchester United.
United snared Lukaku from Everton in a move reportedly worth an initial £75million on Monday, the striker signing a five-year contract with an option of a sixth.
That followed Rooney making an emotional return to Goodison Park by moving in the other direction, 13 years after initially leaving for Old Trafford, where he became the club's all-time record goalscorer.
Rooney, 31, believes Lukaku has the ability to succeed for Jose Mourinho's side, but must avoid self-doubt if he is to handle the scrutiny of playing for such a massive side.
"Playing for Manchester United is a test of character," Rooney, who scored a wondergoal in his second Everton debut against Gor Mahia on Thursday, told reporters.
"You've got to be strong enough mentally to accept the challenge. 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."
Rooney believes it is increasingly difficult for players at United to live up to the standards required now that Alex Ferguson and the famous Class of '92 have moved on.
He continued: "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 any more. I'm just ecstatic to be back at Everton."