Bookmaker William Hill said half of all the money staked on the show has been for a win by the fighter who retained his IBF and WBA super middleweight titles earlier in the year against George Groves, with his price now at 5-1, from an initial 14-1.
Actor John Partridge is the favourite to triumph in the new series, at 4-1, which will see stars tackle a variety of gymnastic disciplines, under the eye of judges such as Louis Smith and Nadia Comaneci.
Other fancied contestants include former Blue Peter host and actor Peter Duncan at 11-2. He is the oldest figure in the competition at 60, after TV fitness guru Mr Motivator - a year his senior - was forced to withdraw after dislocating a knee in training.
The new Saturday night series will also feature former Sugababe Amelle Berrabah, Lucy Mecklenburgh who features in The Only Way Is Essex and ex-Girls Aloud singer Sarah Harding.
The bookmaker is giving figures of 4/6 that Tumble does not get commissioned for a second series.
"It is hard to imagine Tumble being a ratings smash but all will be revealed on Saturday night," said Hill's spokesman Rupert Adams.