No let-up in games for in-form Manchester United striker Romelu Lukaku

Romelu Lukaku has made an impressive start to life at Old Trafford

Romelu Lukaku will have to cope with Manchester United's relentless fixture schedule as Jose Mourinho cannot afford to rest him until Zlatan Ibrahimovic returns .

A summer target for former club Chelsea, United moved quickly to sign the 24-year-old striker in a deal that is already proving smart business - and even good value despite the fact Everton's coffers could eventually be boosted by £90million.

Lukaku made it 10 goals in his first nine United games with a brace in Wednesday's 4-1 victory at CSKA Moscow in the Champions League and, despite only landing in the early hours of Thursday morning, is set to start again on Saturday afternoon.

The in-form Belgium striker can match Andrew Cole's club record of seven goals in his first seven Premier League matches against embattled Crystal Palace, before attention turns to international matters with Belgium.

Roberto Martinez's Red Devils have already qualified for the World Cup so it might be a chance to take things easy on Lukaku, whose role for Mourinho's Red Devils will be far more important until Ibrahimovic returns from his long-term knee injury.

"Look, in here without Zlatan we cannot rotate the striker, especially because Marcus Rashford is playing also in other positions," Mourinho said, with Lukaku having so far only missed the Carabao Cup win against Burton.

"So until the moment we have Zlatan we cannot think about giving rest to our number nine the same way we give in other positions. We cannot do that.

"Belgium is Roberto's responsibility and it's his decision to play him or not to play him."

L ukaku's importance for club and country underlines how he has kicked on since his time under Mourinho at Chelsea, continuing what the Portuguese calls a "global evolution" that has typified his career to date.

"I think every step in his career he got it, he grabbed it with both hands," the United boss said.

"Since his first loan to West Bromwich Albion, he grabbed the opportunity with both hands, fighting for his evolution.

"He was very strong in his desire to be playing in a team with other objectives now, with Champions League football - it was always his dream to come to this level and since he arrived I don't think he thinks in another thing than in his success.

"So he works hard, he rests, he has a great professional life outside the football pitch.

"He has ambitions, he enjoys, so I think it's a global evolution.

"I wouldn't be fair if I wouldn't say that every step in his career with different managers, with different fellow players, with different teams were not contributing to what he is now.

"And now, of course, I think Manchester United is a different level of expectation and he's coping well."

Coping is what United are having to do when juggling domestic and European exertions.

While irked by the ongoing scheduling issues impacting teams in continental action, Mourinho did not want to be seen as moaning as it "doesn't give me solutions".

Instead, he spoke about the importance of mental preparation for weekend games such as Saturday's match against struggling Crystal Palace.

"Your colleague was basically saying that we have good results because we are playing against bad teams, so how can we be excited with what we are doing if we are doing that just because we are playing against bad teams?" he asked, having been annoyed by an earlier suggestion that United have had a kind schedule to date.

"I don't think Everton, West Ham, Leicester will be happy with that, but, okay, we have our feet on the ground.

"We are humble, we know that the great teams of the Premier League we didn't play them yet, so we are calm, we follow our work."