Johnny Manziel wasn't just ordering drinks at a Texas nightclub Thursday night ... he was pouring 'em ... tending bar like a champ and TMZ Sports has the pics.
Manziel hit up Rooftop on 6th -- it only has 2.5 stars on Yelp -- and got behind the bar to sling drinks to some of the patrons.
Sources at the bar tell us Manziel worked the bar for about an hour -- and actually mixed and poured drinks. Apparently, he takes his work seriously.
Eventually, Johnny rejoined the crowd -- and spent some time in a VIP area the bar set up for the Cleveland Browns QB and his friends ... and shocker, we're told Johnny drank champagne.
After the Austin trip, Manziel jetted over to Vegas ... where according to Norm Clarke, the football star stayed at the Real World suite at the Hard Rock, ate dinner at STK and partied at XS nightclub at the Encore.
62 days 'til Cleveland's first regular season NFL game -- plenty of time to shake the hangover, right?!