As you know, Zuck's moved on from a fight with Elon, saying last Friday, " ... I'll share details on my next fight when I'm ready." So, he's got some plan for his "next fight."

He went on to say, "I want to do it in a way that puts a spotlight on the elite athletes at the top of their game," adding, "You do that by working with professional orgs like the UFC or ONE to pull this off well."

Zuck said Monday, "I'm going to focus on competing with people who take the sport seriously."

So, who are the "elite athletes" and "people who take the sport seriously?" It seems unlikely there's another Elon out there -- billionaire vs. billionaire -- and it doesn't make a lot of sense Zuck would involve the UFC for some amateur fight with a rando.

We know Zuck's been in communication with UFC Prez Dana White for well over a month and probably a lot longer, and Dana has 500 fighters on his roster who would love this kind of attention -- fighting M.Z.

Now there's no way Zuck would fight a UFC vet, but what about a fighter who just joined the org?

We contacted Dana with our connect-the-dots theory, and here's what he told us ... "I have said since day 1 Mark is a very serious guy. He loves the sport and is training hard. I believe he is serious about fighting in the UFC."

Notice Dana said "fighting IN the UFC." That more than suggests he'd be fighting someone on the INside, not the outside.