Lukaku linked up with the Baggies on a season-long agreement last summer, with Chelsea prepared to let him head out in search of regular first-team football.
The Belgium international, who had been left frustrated on the fringes of the fold at Stamford Bridge, has impressed during his time at The Hawthorns - netting nine times in the Premier League.
West Brom are known to be keen on keeping Lukaku past the end of his loan deal, although the 19-year-old forward recently expressed a desire to return to West London in the summer.
It was suggested that a clause in his contract would be triggered if he appears in a certain number of games, allowing him to stay on for the 2013/14 campaign.
Clarke has, however, moved to bring an end to those rumours by making it clear that any extension would have to be negotiated with Chelsea.
"That is ridiculous," he said when pressed on a possible contract clause.
"He is simply here on a season-long loan from Chelsea. Nothing else."
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