The free-scoring Belgian is in fine form and leads the Premier League with 24 goals sparking suggestions the Toffees could be looking for as much as £100million if they choose to sell the 23-year-old this summer.
But Koeman says PFA Team of the Year member Lukaku, who is yet to commit his future to the club despite being offered terms that would make him the highest-paid player in Everton history, has more to his game than just finding the back of the net.
"He has scored 24 goals and with five games to go he can reach a really high total," said Koeman. ""It is like for any player who is performing at a high level - every team likes to have goalscorers in the team because goals make points for the team.
"But I think he is improving in the rest of his football. He is doing better pressing and running in the channels.
"He is now a better striker for the team than he was last year.
"I've had several conversations about how, in my opinion, he needs to play as a striker and he is working hard and improving.
"If someone is interested for sure they will call the board and then we will speak about it but we will try to do everything to keep him at Everton next season."