Yup, NFL lineman Jordan Mailata can still REALLY sing ... his Eagles squadmates filmed him belting out "Tennessee Whiskey" at a team meeting this month -- and it's downright incredible!!

The 6-foot-8, 346-pound tackle has never been shy about showing off his voice ... and he did it again this week in front of teammates who couldn't have been more impressed.

Check out the video filmed by linebacker Shaun Bradley -- despite not being a rookie anymore, Mailata grabbed the mic at Philly's "Rookies Sing" event and absolutely slayed Chris Stapleton's classic tune.