MANCHESTER -- Jose Mourinho believes Romelu Lukaku will find it hard to match Wayne Rooney's goalscoring exploits at Manchester United because the Premier League is tougher now than it was when the former England captain was at his peak.

Lukaku and Rooney will come face-to-face on Sunday for the first time since swapping clubs in the summer.

Rooney left Old Trafford as United's record goalscorer with 253 in all competitions over 13 seasons. Lukaku, meanwhile, has made a flying start to his United career with six goals in as many games.

Speaking at a news conference on Friday, Mourinho said it is unlikely Lukaku will be able to challenge Rooney's record given the former club captain arrived at Old Trafford when he was a teenager.

But the Portuguese coach also believes the Belgian, 24, is playing in a more difficult league than United's former No. 10.

He said: "I think Wayne spent probably 10 years of his career in a different Premier League than you have now.

"A Premier League where it was easier to score goals not just because of the difference between the top teams and others but also because of the profile and the tactical interpretation of the competition.

"I think this Premier League is much more defensive-minded, and much more difficult."

Romelu Lukaku and Wayne Rooney will face off for the first time since swapping clubs this summer. BEN STANSALL/AFP/Getty Images

Lukaku's goals have helped United score 16 times in six games so far this season. It is in contrast to Everton, who have not found the net in any of their last three fixtures.

United finished the last campaign as the lowest scorers in the Premier League's top seven with just 54 goals. And despite a positive start to the new season, Mourinho wants more.

He said: "I am very pleased with the contribution but I want more goals.

"The way the team plays, they have to. When a team doesn't create a lot, when a team doesn't have the ball, when a team is just reactive, it is more difficult for these players but when the team is in control and makes decisions on the direction of a game, when the team is so offensive, when the team puts so many people in attacking areas, I think they have to score goals."

Mourinho will be without Paul Pogba against Everton after the midfielder was ruled out with a hamstring injury with Marouane Fellaini one of those in line to take his place.

After giving away a penalty in the 1-1 draw with Everton at Goodison Park last season, Fellaini was booed by some United fans during the next home game against Tottenham.

But after replacing Pogba against Basel on Tuesday, the Belgian was voted man-of-the-match after scoring the first and making the third in a 3-0 win.

Mourinho said: "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 Jones, he made a bad mistake for Stoke's second goal. 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 from the media.

"It's just being pragmatic and showing common sense."