The 19-year-old has completed a season-long loan move to the Hawthorns from Stamford Bridge, and Clarke has admitted that Lukaku's hunger to improve as a player at West Bromwich Albion helped him seal the move.
Clarke told the Birmingham Mail: "He's a big strong player. His goal record before he went to Chelsea was very good.
"What I like when he got here was that he has already asked for extra shooting practice and he hasn't even started training yet.
"It shows he has got hunger and I was impressed when I spoke to him."
Lukaku joined Chelsea from Anderlecht for £18m last summer.