Ronald Koeman: Everton must tighten up in order to stop Romelu Lukaku
Ronald Koeman has warned Everton that their former star Romelu Lukaku's purple patch will continue if they do not improve defensively at Old Trafford.
Belgium international Lukaku left Goodison Park for Manchester United this summer in a £75 million deal after scoring 20-plus goals in each of his previous three seasons with Everton.
The 24-year-old already has six in as many games for his new club and Koeman stressed that the Merseysiders, struggling for form, must tighten up.
"We know him really well," Koeman said of Lukaku. "He's one of the best strikers.
"I mentioned several times last season that he's a great finisher. I hope that we know how we have to defend against him.
"There are a lot of individual qualities in the players around him. In the box he's really dangerous, he's fast, he's strong.
"If we defend how we've defended in the last few games, then maybe it will be his afternoon."
In a busy summer during which Koeman overhauled his squad, the transfer window closed without the manager having landed a replacement for Lukaku, who scored 25 of their 62 Premier League goals last term.
Ex-United forward Wayne Rooney is the only player to have found the net for Everton in their opening four top-flight fixtures, and Koeman accepts that current strikers Dominic Calvert-Lewin and Sandro Ramirez, 20 and 22 respectively, cannot be asked to assume Lukaku's role.
"There's no frustration now because you can't do anything at this time," Koeman said of failing to add another attacker.
"We have different types in Dominic and Sandro. Sandro needs time to adapt to the Premier League. Yes, he has pace but he's not physically the strongest.
"But it's too easy to mention the strikers. Defensively we are making too many mistakes."
Koeman has been impressed with the United side Jose Mourinho has built for this season and is expecting a tough test.
"It's how you look at it -- maybe it's good that in the last three seasons I've had good results at Old Trafford [with Southampton and Everton]," he said.
"But Manchester United are really strong, a stronger team than last season, and at the moment we're not at the level we were last season."