Bosses had hoped Celine would perform with Sharon Osbourne's protégée as part of the traditional star duets, but according to The Sun, the 'My Heart Will Go On' singer has said she is "too busy".
Producers are now trying to find another star to sing with Sam at the final, due to take place on the weekend of 14 and 15 December at Wembley Arena.
The stars who will be dueting with the finalists will be announced next week.
Four contestants currently remain in the competition and will be fighting it out for a place in the finale as they take on the songs of Beyonce and Elton John this weekend.
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