Morgan Wallen Falls Hard Onstage During Concert

Morgan Wallen is having zero problems filling stadiums with fans wanting to see him on his new tour ... his onstage navigation, however, is a whole other issue.

Wallen was in Louisville, KY at the KFC Yum! Center Thursday night during a stop on his One Night at a Time World Tour. In video, obtained by TMZ, Wallen's belting out his hit "Heartless" -- one of the final songs in his set -- when he takes a nasty spill.

It's pretty clear how it happened, you can see a ton of fog near Morgan's feet ... likely making it next to impossible to see where he was walking. On top of that, people at the show tell us there were some technical issues with the lighting along the bottom of the stage as well.

Lucky for both Morgan and the rest of his fans with tickets to his upcoming shows -- he almost immediately bounces right back up -- and seemingly without any injuries ... not to mention, he didn't miss a note.