Caitlyn Jenner -- Gamble On My Boobs ... Prop Bets Over Espy Outfit

Cleavage or no cleavage ... that is the question when Caitlyn Jenner takes the stage at the ESPYs this week and the answer could make you serious money ... TMZ Sports has learned.

Jenner's boobs are the center of a prop bet on BetOnline.ag -- the same site that took action on Katy Perry's breast situation during the Super Bowl halftime show.

Of course, Jenner is set to receive the Arthur Ashe Courage Award at the ESPYs on Wednesday ... and the odds say she is LIKELY to show off the gals when she gets her trophy.

In fact, the odds are so stacked ... pro-cleavage bettors need to wager $260 to win $100.

It will definitely be interesting -- Caitlyn's been all over the place with her fashion choices lately ... but as one person in our office put it ... "She didn't buy those things to keep 'em covered up."

Good luck!