The hopeful claimed that he has had messages from people saying they will "bottle" him.
"I've had death threats, I've been told I'm going to be bottled and my face sliced open," The Sun quotes him as saying.
"At times it has killed me and it's disgusting - some of these people act like I'm a murderer. It has made going out in public quite daunting."
Clark added that the threats have given him concern over his ill mother, saying: "My mum's not silly, she knows not everyone will like me.
"But reading comments threatening to break into my house and firebomb me would shock anyone."
The singer recently hit back at his critics, telling them to "go and have a w**k".
Clark will discover whether he has made the final shows during tonight's second Judges' House episode of The X Factor (September 30).
Picture gallery - X Factor Judges' Houses final decisions:
Copyright: THAMES TV/SYCO