Mayweather/McGregor celeb fans are gonna be screwed out of prime Strip parking if they swoop in last minute ... because Vegas doesn't want the private jet s**t show that went down for Mayweather's last fight of the century.

You'll recall the famous pics of McCarran International Airport tarmacs choked with PJs in 2015 for Mayweather/Pacquiao. That traffic jam taught 'em a lesson. Airport sources tell TMZ, McCarran's implemented a reservation system.

The bad news for latecomers ... the lot's just about full. We're told McCarran is capping the number of birds allowed to park this weekend. Last minute arrivals will still be allowed to land, but will have to bolt after dropping off celebs.

That means anyone looking to flee at a moment's notice will be screwed. Ya can't call 'em to fuel up the jet, if the jet ain't even there. There is a plan B ... reserve parking at one of 2 nearby municipal airports.

Of course, they'd lose the joy of taxiing a G5 past Southwest jets packed with normies, and also would NOT be Strip adjacent -- but even filthy rich beggars can't be choosers.