Mourinho has told United goal machine Lukaku he can’t afford to ease up until Zlatan Ibrahimovic is available.
“Without Zlatan we can’t rotate the strikers,” Mourinho revealed. “Also because Marcus Rashford is playing in other positions.
“Until the moment we have Zlatan we can’t think about giving rest to our number nine the same way we give in other positions. We can’t do that.”
Discussing Lukaku’s improvement since their time together at Chelsea, Mourinho was reluctant to judge.
“I don’t want to speak about this progress because if I do that it looks like we have done something extraordinary in three months – something he hasn’t done in the other years of his career.
“It’s not fair. It’s been about evolution. I think every step in his career he has got it, he has grabbed it with both hands since his first loan to West Brom. He grabbed the opportunity with both hands, fighting for his evolution.
“He has been very strong in his desire to be playing in a team with other objectives now. Champions League football was always his dream – to come to this level. Since he has arrived here I don’t think he has thought anything other than to be a success.
“So he works hard. He rests. He has a great professional life outside the football pitch. He has ambitions. He enjoys this. I think it’s been a global evolution.
“It wouldn’t be fair if I didn’t say that every step in his career, with different managers, different fellow players, different teams hasn’t contributed to what he is now. Now I think that Manchester United of course is a different level of expectation and he is coping well.”