Greg Hardy vs. Shawne Merriman ... in a fist fight?!
Yeah, this could actually happen.
Shawne -- the former NFL superstar -- is about to compete in his first bare knuckle boxing match ... and if he wins, "Lights Out" says he'd LOVE to get in the ring against Hardy.
Of course, Hardy has been crushing everybody since transitioning from the NFL to MMA -- and has already earned a development contract with the UFC.
Now, Merriman is following Hardy's lead .