There's a Johnny Manziel connection to the Mayweather vs. McGregor fight -- his fiancee is one of the Corona Girls!

TMZ Sports has learned ... Bre Tiesi (who happens to be a smokin' hot model) was tapped to don the legendary Corona outfit to work Friday's weigh-in festivities

She did an excellent job!

No word if Johnny plans on heading to Vegas to attend the fight -- or if he's busy training for his NFL comeback. 

One thing's for sure ... Bre looks goooood!!!