José Mourinho believes Wayne Rooney’s record 253 goals for Manchester United may be impossible for his replacement Romelu Lukaku to overhaul.

Rooney makes a first return to Old Trafford in Sunday’s late kick-off since departing for Everton on a free transfer in the summer, with Lukaku moving the other way for an initial £75m.

Rooney spent 13 years at United, having joined from Everton at the age of 18, while Lukaku was 24 on his arrival. The Belgian has scored six in six appearances in all competitions. Asked if Lukaku could threaten Rooney’s record should he stay at United for the next decade or so, Mourinho said: “Wayne arrived much earlier [in age]. He spent probably 10 years of his career in a different Premier League to the one you have now, where it was easier to score goals. [Also] the difference between the top teams and the others [and] the profile of the competition. Now it’s much more defensive and more difficult.”

Mourinho believes Rooney will receive the reception he is due. “I think he’ll get the welcome he deserves,” the United manager said. “Sometimes the word legend comes too easily but he’s a real legend of the club. The number of appearances, goals, trophies – clearly he’s one of the most important players in the history of Manchester United. I think the stadium will show him the respect he deserves. I hope before the match and after but not during it.”

Rooney played 559 matches for United and won five Premier League titles, the Champions League, the Europa League, the FA Cup and three League Cups, and was voted the 2010 PFA and Football Writers’ player of the year.

Last season he lost his starting place under Mourinho. Yet the manager would not be drawn on whether Rooney, who is now a regular at Goodison Park, has benefited from his move. “He is an Everton player but I’m not going to speak more,” he said. “He’s a legend, he deserves to be welcomed that way but during the match he’s an Everton player.”

Zlatan Ibrahimovic scored 28 times for United last season before suffering a serious knee injury. Lukaku’s strong start suggests he can emulate the Swede though Mourinho is unsure if the striker can propel United to a 21st title.

“Last season we had a very good striker for two thirds of the season and it was not enough to win the title. It’s only the second year [of my tenure],” he said. “Romelu has a better team than Zlatan had. He plays a different style and the confidence levels are different. But he deserves credit for that start. The way he plays, the way he’s committed, his overall contribution, we couldn’t be happier.”

Mourinho did not wish to consider parallels between Ibrahimovic and Lukaku. “I’m not going to compare,” he said. “It’s very stupid to compare. When players are so different there is no point.”

Last season Mourinho repeatedly called on Jesse Lingard, Anthony Martial, Henrikh Mkhitaryan and Juan Mata to add goals. Of the quartet only Mkhitaryan has scored this season and the manager said: “I’m very pleased with the contribution but I want more goals. The way the team plays I think they have to, when a team doesn’t create a lot, doesn’t have the ball, when it’s just a reactive team, it’s more difficult. When a team makes decisions and puts players in attacking areas, they have to score goals.”

In last December’s fixture at Goodison Park Marouane Fellaini conceded an 88th-minute penalty which Leighton Baines scored and the game finished as a 1-1 draw. Yet the Belgium midfielder’s importance to Mourinho was underlined in him coming on for the injured Paul Pogba and scoring the opener in Tuesday’s 3-0 Champions League win over Basel.

“His mistake last season was the kind of mistake that I accept in a player. I accept the goalkeeper that concedes a bad goal. I accept the player who misses a penalty. I accept the player who makes a mistake and gives a penalty away. I accept all these individual mistakes that are part of the game and part of football players. What I did with Marouane is what I do normally with every player.

“Like Phil Jones, he made a bad mistake for Stoke’s second goal [in last week’s 2-2 draw]. Did I kill him? No. Will he be on the bench on Sunday? No. So life goes on, and that’s the way I did it last season with Fellaini. When players make one individual big mistake and everybody knows that they did it, the players are the first to know they did, and they don’t need any more criticism from the manager that they get from the fans or the media. It’s just being pragmatic and showing common sense.”