Elon Musk-Mark Zuckerberg Weight Difference Holding Up MMA Fight

Conversations continue between Elon Musk, Mark Zuckerberg, and Dana White ... and while the billionaires are itchin' to get their hands on one another, there's is an issue preventing the fight from being made official -- Elon's weight advantage.

Our sources tell us the guys are still serious about fighting in an Octagon, and as the UFC president told us yesterday, he's absolutely down to put on the fight ... but, Zuckerberg's size disadvantage has become an issue.

In fighting, size matters, a lot. Elon is 6'1", and reportedly weighs between 185 and 200 lbs. As for the Facebook founder, he's just 5'7", and reportedly weighs around 155 lbs.

Significant differences ... Elon has a 6-inch height advantage, and somewhere around a 30 to 45 lb. weight advantage.

To put that into perspective, Zuck would be a lightweight in the UFC. Musk would be a middleweight or light heavyweight ... a 2-3 weight class difference.

Typically, exhibition fights ignore weight classes ... Floyd Mayweather has fought a much bigger Logan Paul, for example.

But, just because the fight could technically be made doesn't mean Mark isn't hesitant to give up a sizeable advantage to his foe.

On Thursday, White joined "TMZ Live" and revealed he'd actually been having conversations with both men, who Dana says are "absolutely dead serious" about fighting in an Octagon.