The singer is said to have received a steady stream of death threats on Twitter since last weekend's results show, which saw him saved over Carolynne Poole in a Deadlock decision.
However, his fellow finalists have got behind Clark by giving him a standing ovation in dress rehearsals yesterday, reports The Sun.
A show insider said: "The others have been very worried about him. He has been really down and getting a stream of death threats and hateful messages on Twitter.
"He is convinced he will get the boot tonight. But his fellow contestants have pledged to give him round-the-clock support - they all love him."
> X Factor show two: Who sang best? Have your say - poll
Clark performed a cover of Gary Barlow's Take That hit 'Back for Good' as part of a medley of songs.
He previously spoke about receiving death threats from X Factor viewers before the live shows began.