Everton manager Ronald Koeman believes Romelu Lukaku needs to improve his workrate if he wants to become a "top striker."
Lukaku, 23, has impressed for the Toffees this season, having scored seven goals and registered four assists in 11 appearances.
However, Koeman believes the Belgium international can still better himself as a forward by working harder for the team.
"I understand it is difficult because we need to press more and they need to change their attitude -- like Romelu," Koeman told a news conference.
"I can't advise him on finishing in the box because I was not a striker and he is one of the best finishers I have ever seen in football.
"But I can teach him how he needs to press, how he needs to run, and how he can make it difficult for the defenders of our opponents.
"If he wants to be that top striker, he needs to improve that aspect."
Koeman stressed on Friday how important it is for Everton to retain the services of Lukaku for "as long as possible."