Thirteen years after quitting Everton to join United in a £26million deal, Rooney has returned to his spiritual Merseyside home, while Lukaku has moved in the opposite direction for £75m.
Now, the former England captain has lifted the lid on the unique demands that the Belgium striker will face as Old Trafford’s top talisman.
And he revealed how Class of ’92 graduates, such as Ryan Giggs, Gary Neville and Paul Scholes, played a crucial role in his development from teenage prodigy to United’s record goalscorer.
Asked to offer Lukaku some words of advice, Rooney said: “There are standards that you have to keep when you are at Manchester United.
“That came from the manager Sir Alex Ferguson when I went to United and it was then passed down through the dressing room by the likes of Giggsy, Gary Neville and Scholesy.
“Over the last few years, it was down to me and Michael Carrick to keep the new players maintaining those standards.
“That became 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’s become harder, but that’s not my problem any more. I’m just ecstatic to be back at Everton.”
Rooney marked his United debut with a Champions League hat-trick against Fenerbahce – and never looked back. With Carrick, the 31-year-old is the only Englishman to have won the Premier League, Champions League, Club World Cup, Europa League, FA Cup and League Cup.
And he also took Sir Bobby Charlton’s goalscoring records for both club and country. Now, Lukaku must fill the boots he has left behind.
Rooney said: “Playing for Manchester United is a test of character, as well as your ability.
“You have got to be strong enough mentally to accept the challenge because United is 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, he will be a success. But if he doesn’t face the challenge, if he worries about things, then it will be more difficult for him.
“Hopefully, Romelu has got people there who will give him the right guidance and get the best out of him.”
Rooney intends to add to the 15 medals he won at United after revealing that he had other offers, which would have made him more than the £300,000 a week he will bank at Goodison, following Everton’s agreement to meet the terms of the contract he was on at Old Trafford.
“To be honest, it would have been easy for me to sit at Man United, sit on the bench like I did last season, pick up my money and see you later. But I am not that kind of person,” he said.
“I could have also got more money at different football clubs other than here, but I really need to play and I need that challenge.
“I don’t just want to play and not care whether we win a trophy or not. I want to play and be successful. Ronald Koeman and the club have shown me the ambition of where they want to go.
“It was perfect for me to come back. Obviously, there will be a lot of pressure on me, but I’m ready for that.”