Heavyweight Champ Deontay Wilder says there's only one UFC fighter he'd like to get in the boxing ring ... and it ain't Conor ... telling TMZ Sports he'd love to kick the hell out of Brock Lesnar.
We got the big man out at LAX and wanted to know which Octagon star he'd like to rumble with ... since boxing vs. UFC is all the rage these days.
He totally disses McGregor ... saying he's too small and not skilled at all .