Clarke feels Lukaku has made huge progress.
He said: "I've seen a boy who came here with little confidence, apart from the fact that he had been bought for a lot of money.
"He hadn't many chances to play. Now he's got more confidence, his touch is improving. His work-rate is getting better.
"It can improve still further but he's a handful for defenders, he still has a knack for scoring goals. It'll be down to him how he works in training.
"And down to me to decide whether I can go with two strikers or one striker or a rotation policy.
"But it's not fair to compare him to Didier Drogba. He's Lukaku."