The four-part series is set to air later this year on Channel 4 in aid of the Stand Up To Cancer campaign.
While the Sky News presenter was said to be part of the line-up, she has now withdrawn, according to The Sun.
The publication reports that Kay signed up to the programme believing there was no competitive element.
A spokesperson told them: “It is a cause close to her heart and swimming the Channel was a challenge she wanted to face.
“But after passing the medical, it became apparent the nature and format was not how it had been described.”
Meanwhile, Channel 4 spokesman said: “All celebrity contributors were fully aware when signing up for Sink Or Swim what the process entailed.
“It is not, and has never been, a competitive show and has no formatted elimination.”
Express.co.uk has contacted a representative of Kay’s for comment.
The famous line-up is also set to include Simon Webbe, Linford Christie, Sair Khan, Alex Brooker, Georgia Kousoulou, Wes Nelson, Rachel Adedeji and James “Arg” Argent.
The broadcaster say the programme “attempts to erase the stigma of being a non-swimmer and follows the progress of a cast of famous faces – complete non-swimmers themselves, those with a fear of open water or those who have been taught to swim as children but now struggle to do so for health reasons – as they are pushed to their absolute limits.”
Steven Handley, Commissioning Editor for Entertainment at Channel 4 said: “Sink or Swim promises to be one of the most perilous Stand Up To Cancer Celebrity Challenges we have ever attempted.
“It will push the boundaries of what Celebrities will endure and overcome to raise money and awareness for charity and we are delighted to be working with TwoFour on this ambitious project.”
Elsewhere, Mel Leach, Executive Producer for programme makers Twofour stated: “Swimming the Channel is a monumental feat for even the very best swimmers, let alone those who can’t even swim a length.
“Our brave celebrities will have to overcome their fears and embark on a huge mental and physical transformation to complete this epic challenge.”
Kay suffered a bit of an embarrassing blunder last week with her use of an emoji on Twitter.
It came as a social media user asked the Sky News anchor if she would be paragliding “without a harness” and added they “hoped so”.
Kay retweeted the post and vented: “Wonder how brave keyboard warriors would be if they were face to face with my 6′ sons and his mates.”(sic)
However, she added an aubergine emoji onto the end of the message, which is commonly used as a substitute for a penis.
Many responded to the now-deleted tweet to point out to Kay that she may have used the emoji incorrectly.
One person joked: “Just out of curiosity… how do you know his mates’ [aubergine emoji] are so impressive?”
“I reckon I could take him. No issue with you, just want to fight a six foot aubergine,” a second added.
While a third person commented: “Placement of the [aubergine] emoji here raises a lot of questions I don’t want answers to.”
Sink or Swim will air later in the year on Channel 4.
