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 ... sorta.
The ex-Chargers Pro Bowl linebacker signed a deal with the World Bare Knuckle Fighting Federation to brawl on Nov. 9 against Mike Bourke -- a dude who once knocked out Ken Shamrock.
If Merriman wins, he tells TMZ Sports ... a superfight with Hardy would be awesome.
"I'll definitely be open to see what Greg Hardy got to offer."
By the way, this isn't some fun experiment for Merriman -- he's been seriously training for years and believes, since he's only 34, he can have a real future in combat sports.
It all starts with Mike Bourke -- and Shawne says he's already putting together his fight plan.