Lukaku was dropped for last night's Champions League win against Lille.
Melchiot said, "He's a great player, I said that when Chelsea were interested in him and I will not change that opinion. He has to find the space and the freedom he's looking for; with his back to goal, if he holds onto the ball too long, he can't get through.
"I think he has to change his game a little bit. Kai is not that player; he's not built that way, but I'm surprised he's so good at turning and facing the opponent's goal so quickly because he is so tall.
"Normally, you have a small guy. Barcelona played that system under [Pep] Guardiola, the false 9. Havertz doesn't look like a false 9 but he is because he drops off and finds the pockets. Tuchel is building a system where if Lukaku isn't doing what he wants him to, he can play the other guy."