Manchester United cannot rest Romelu Lukaku until Zlatan Ibrahimovic is back fit and available, manager Jose Mourinho said.
Lukaku has made an impressive start to life at United, scoring 10 goals in nine games in all competitions since arriving from Everton.
It is expected Ibrahimovic will return from his knee injury in January, sure to provide high-flying United with another boost.
Mourinho, whose team host Crystal Palace on Saturday, said it would be up to the 24-year-old Lukaku to continue delivering until Ibrahimovic was available once more.
"Without Zlatan, we cannot rotate the striker, especially because Marcus Rashford is playing also in other positions," he said.
"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."
Lukaku has shown no signs of slowing down for United, although he also has Belgium's upcoming World Cup qualifiers to contend with.
Mourinho refused to take credit for the striker's stunning start at United, saying Lukaku had always made the most of his opportunities.
"I don't want to speak about his progress," he said.
"If I do that, it looks like we did something extraordinary in three months that he didn't have in the remaining years of his career.
"I don't think it's fair. It's just a global evolution. I think every step in his career he got it, he grabbed it with both hands."