The Belgium international, who is on loan at the Hawthorns, scored the winning goal on his full debut for the Baggies in their 1-0 victory over Reading on Saturday.
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"If he scores 20 goals by Christmas and Chelsea want him back, there's not a lot I can do," Clarke told reporters.
The former Anderlecht forward, meanwhile, reiterated that he had not been put off having a future at Chelsea despite the limited opportunities he received in the season that followed his multi-million pound transfer.
"My dream is to play for Chelsea," he said. "I just want to make the best out of my career."
Lukaku is only 19 years of age but hoped that, in the meantime, he could continue to prove that he was ready for a role of responsibility at West Brom.
"I'm just 19 and people will still look at me like a baby," he added. "But I want to play as much as I can."