Forget GGG-Canelo and Conor-Khabib ... the fight EVERYBODY wants to see just took a real step toward happening -- 'cause Greg Hardy is ALL IN on a fight with Shawne Merriman!!
Remember ... the ex-Chargers superstar told TMZ Sports he's down for a fight with Hardy if he wins his first tilt in the World Bare Knuckle Fighting Federation in November.
Well ... Greg just got word of the challenge -- and says he's DEFINITELY in for the match.
"All I’m saying is if you like entertainment as much as I do, you would def enjoy this one," Greg says.