Donald Trump and Conor McGregor in the same building??
It could happen on Saturday ... because the President-elect had told Dana White he'd be at UFC 205 if he won the election.
We spoke with Dana -- who famously gave a speech for Donald at the Republican National Convention back in July -- and the UFC honcho told us about Trump's tentative plans to attend the fight in NYC.
"Donald originally told me he that would come to the fight if he won," White said.
"I don't think Donald really realized what his duties were gonna be had he won. I think he's meeting with Obama today and then I don't know. We'll see, man."
"Listen, no pressure to come ... but it wouldn't suck if he came."
White says Trump's family not only called him after the election -- but invited him to the victory party. And you bet your sweet ass White got out of bed and went!