The boyband star revealed on Twitter that he has been in bed for the last 36 hours after getting food poisoning.
[Union J left to right - JJ, George, Josh, Jaymi]
"Haven't left my bed for the last 36 hours with food poisoning. Been SO ill!! Sorry for lack of tweets :( josh xx," he wrote.
"Owwwww food poisoning from that Chinese takeaway I had :( :( :( still feeling awful. Worrying about tomorrow night now :( josh x."
His band mater George Shelley tweeted: "Josh has just passed out again! Let's give him support to make him feel better #GetWellSoonJosh."
Jaymi Hensley revealed that he was making breakfast in bed for his bandmate, while JJ Hamblett added: "Praying Josh is better for tomorrow night."
Union J's Cuthbert joins Lucy Spraggan on the X Factor sick list. Spraggan missed last Saturday's show due to ill health and it's rumoured to be touch and go as to whether she can continue in the competition.
The X Factor Live Shows continue this weekend on ITV1.
Watch Union J's performance of 'Call Me Maybe' below: