Stipe Miocic is returning to the Octagon after almost 4 years away for a fight against the legendary Jon Jones ... in front of a packed crowd at Madison Square Garden that could include President-elect Donald Trump!

With the UFC's heavyweight title on the line ... we asked 42-year-old Miocic whether he'd be down for 45 (& soon-to-be 47) to play Dana White for a night, and wrapping the belt around his waist if he defeat Bones.

"I'm not against it," Stipe responded, saying, "That'd be kinda cool to have a president do it. President-elect."

Miocic then looked to someone in the room with him and asked, "[Trump's] gonna be there, right?" ... which they confirmed.

It lines up with what Michael Chandler, who is also on the card fighting Charles Oliveira in the co-main event, told us on Thursday ... saying DJT told him he'd be at UFC 309 if he won the presidential election.

Of course, President Trump won by a landslide, taking not only the Electoral College (which determines the winner), but also the popular vote.

FYI, Miocic is a blue-collar guy from Ohio (a solidly red state) -- but he's not overly political.

Stipe, however, has occasionally commented on Trump in the past ... including when DJT was nearly killed in an assassination attempt in Butler, PA, on July 13.

If Trump makes a cameo at the World's Most Famous Arena, it won't be the first time he's shown up this year to support his close friend Dana's business.