The powerful teenage forward has been a revelation at The Hawthorns this season, with regular football allowing him to showcase his true ability.
He has found game time restricted since arriving in English football, with Chelsea initially reluctant to throw him into Premier League life.
It is, however, expected that the Blues will draft Lukaku back into their plans when he returns to Stamford Bridge from a year-long loan over the summer.
Clarke appreciates that there is little he can do to prevent Chelsea from taking the 19-year-old back, with a 13-goal return proving that the Belgium international has what it takes to be a top-flight success.
He said: "He is Chelsea's player. He belongs to Chelsea and he will go back there in the summer.
"I have never thought it would be possible Chelsea would let him come back next season.
"He came on a season-long loan and we're grateful we got him."