NBA's Deron Williams Turned Down Offer To Fight Greg Hardy, Here's Why!

NBA stud Deron Williams was once offered a real-deal fight with Greg Hardy ... and wanna guess what his response was??

Yeah, it was a firm HELL NO.

Deron is actually a pretty legit MMA fighter ... dude has a serious wrestling background and he even co-owns Fortis MMA in Dallas where 3 fighters on the UFC 228 card train.

In fact ... UFC heavyweight Rashad Coulter -- who works out with Williams -- tells TMZ Sports, "He's a good wrestler and has fast hands."

But, when word of those skills got around to the Legacy Fighting Alliance -- where Hardy used to scrap -- they asked if Deron wanted to fight Greg ... D-Will's response was a swift no.

"Are they crazy right now!?" Williams says.

"Greg Hardy has to cut weight to make 265. You think I'm getting in there with that animal!?"

Williams tells us there is one scenario where he might step into the Octagon for real -- albeit not against Hardy -- saying he'd be down to fight one day for charity.

As for his basketball future ... Williams sure seems like he's done with the NBA -- although he ain't officially closing that door yet.