Mettenberger was punched in the face by another bar patron but did not need medical attention, according to Steve Ford, owner of Losers Most Wanted Bar & Grill.
"Here's the truth: The guy said something about 'Roll Tide!' to Zach, and Zach turned around and said, 'Good luck with that,'" Ford told The Tennessean on Monday. "And the guy's buddy then sucker-punched Zach.
"I promise you that Mettenberger did not throw a punch. He didn't do anything. The guy sucker-punched him in the eye, that's the bottom line, and the guy that punched him started running out the door. My door guys had to chase him down."
The Titans selected Mettenberger out of LSU in the sixth round of the 2014 NFL draft. In Mettenberger's three seasons with the Tigers, LSU went 1-3 against Alabama, including a loss in the 2012 BCS National Championship.
The Titans have declined comment on the situation.