Romelu Lukaku was almost impossible to replace at Everton, according to manager Ronald Koeman.
Lukaku, 24, joined Manchester United in July for a reported £75million, ending a four-season stay at Goodison Park.
Koeman, whose team have made a slow start to the campaign and visit United on Sunday, said replacing Lukaku was always going to be a huge ask.
"I don't say impossible but that was close to impossible to get someone in who will score that amount of goals that Romelu scored for Everton," the Dutchman said, via the Liverpool Echo.
"With Romelu we had enough fights about how he needs to press, how he needs to run, how he needs to move but in the box, with opportunities to score, he is one of the best.
"It is always difficult to replace players like him because of the person he was, the physical boy that he is, the number of goals that he scored. It is difficult."
