Forget Gatorade, Conor McGregor's road back to the UFC Octagon is apparently being fueled -- at least in part -- by beer!!

Check out footage TMZ Sports has obtained from the MMA star's sister's wedding earlier this month -- the 36-year-old nearly downed a whole pint of suds in a matter of seconds at Erin McGregor and Terry Kavanagh's ceremony out in Ireland.

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Conor, of course, is currently trying to work his way back to the UFC following a three-year hiatus ... but it's clear he put a pause on his training regimen to celebrate his older sibling's nuptials in style.

In the clip, you can see after a machine created him a custom glass of his own Forged Irish Stout -- he almost took it all down in just one gulp. After tapping out a little over halfway through -- he flashed a big grin showing he was pleased with his results ... all while a foam mustache formed over his lip.

Based on some pics he posted from the festivities, it was hardly the only alcoholic beverage he had on the day -- but it's tough to blame the dude for celebrating ... it was his big sis' big day after all!!

Other attendees certainly partook in drinking as well, take a look at some photos we obtained ... machines spit out Conor's Irish Stout to guests with homages to Erin and Terry all over 'em.

Unclear if it means anything for his comeback fight against Michael Chandler -- which has already been rescheduled once due to a toe injury Conor suffered in the leadup to the planned tilt -- but before fight fans get into a tizzy ... the Notorious One showed it was back to electrolytes and workouts in the days following the party.

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On Instagram, he posted some video showing him beating the hell out of a heavy bag -- proving that the occasional beer here and there hasn't made him any less powerful.