TV bosses are now trying to line up a replacement to take part in the series, which begins tomorrow night.
Celebrities have spent weeks building up the courage to take the plunge from a 10-metre board under the tutelage of diving star Tom Daley.
A source confirmed Metcalfe, who plays Mercedes McQueen in Channel 4's Hollyoaks, had left the show.
She had not been due to appear until the third heat in a fortnight's time, alongside Linda Barker, funnyman Dom Joly, actress Tina Malone, and bookies' favourite, Olympic boxer Anthony Ogogo.
Metcalfe met Longchambon when she was a contestant on Dancing On Ice.
This series he is partnered by Coronation Street actress Samia Ghadie.
The pair have been rumoured to have grown close in recent weeks.