The French maître d' - who made his name sharing love advice with hopeful singles on the Channel 4 dating series - is taking to the dancefloor with pro Dianne Buswell for the festive edition of the BBC ballroom show, and admitted the rehearsals have been gruelling.
Speaking on This Morning, he said: “We trained for four hours. I was bleeding, my feet were bleeding. I went back home and I was vomiting everywhere.
"My body couldn't take it.”
“I lost three kilos in three weeks of training,” he said.
“Now I'm back to my fighting weight."
The restaurateur confessed he was terrified when he got the call inviting him to take part in the show.
"I got so scared," he said. "Because I can’t dance, I can’t dance!"
He said he also had to consider whether he would be able to pull off the performance on the day, or whether he would “freeze and make silly mistakes”.
TV star Sirieix first appeared on First Dates in 2013.
His other television ventures include Snackmasters and Million Pound Menu.
Watch: Fred Sirieix wishes diver daughter good luck at Tokyo Olympics