Rocky drank raw eggs for protein ... but Manny Pacquiáo takes things a step further ... 'cause TMZ sports has learned, the eggs he likes to eat are filled with UNBORN BABY DUCKLINGS.
It's true ... the boiled duck fetuses -- called Balut -- are all the rage in the champ's native Philippines. The little duckies are cooked ALIVE right before they hatch ... and are eaten out of the shell.
Pac-man was at a press conference for his upcoming Timothy Bradley fight in NYC today ... when we asked him if the popular Filipino snack tastes as nasty as it looks.
Check out the clip ... Manny's face tells the whole story.