The 20-year-old fell sick after eating a tuna sub sandwich last night (October 31) and is now an IV drip at an LA hospital, according to TMZ.
Emblem3's Wesley and Keaton Stromberg are said to be rehearsing without Chadwick, and will perform as a duo on tonight's show if necessary.
1432 singer Camila Cabello is also said to be feeling the effects of the tuna sandwiches, which were ordered as a takeaway by a number of contestants and crew members - six of whom are now believed to be out sick.
The X Factor USA's live shows got under way last night, a day earlier than originally scheduled.
The talent show continues tonight on Fox, with four acts due to be eliminated.
Photo gallery - The X Factor USA 2012's opening live show:
Copyright: Fox Brian Dowling