Maloney was reportedly so ill that he was advised by doctors not to take the stage, but persevered to make next weekend's X Factor final in spite of a vomiting bug.
> 'X Factor': The final three - Who should win?
"Chris was very ill, but is a real trouper and went ahead," a source told The Mirror. "He didn't want anything to get in the way of making the final.
"The doctor ruled out food poisoning - it might be the winter vomiting bug. He was in a really bad way."
Maloney, who is mentored by Gary Barlow, will compete with fellow soloists James Arthur and Jahmene Douglas - who are mentored by Nicole Scherzinger - next weekend.
Both Barlow and Scherzinger will sing with their respective acts during the final, it has been confirmed.
The X Factor finals take place next Saturday and Sunday (December 8 and 9) at Manchester Central and will be broadcast live on ITV1.
Photo gallery - 'The X Factor' semi-final results show in pictures:
Copyright: Ken McKay/Thames/Rex Features