UFC's Derrick Lewis to Greg Hardy, If You Beat Volkov, I'll Fight You Next

Derrick Lewis says he's heard all the trash talk; Greg Hardy has been saying about him -- and now he's ready finally settle their beef in the octagon ... with one HUGE caveat.

Hardy is fighting Alexander Volkov in Russia next weekend -- his first fight against a ranked opponent. When we spoke with Greg about it, he told us if Derrick "Pillow Hands" Lewis could knock out AV, he'll be able to do it too.

Hardy also called Lewis "soft."

Obviously, Lewis wasn't amused with Greg's insults -- and fired back ... calling him a woman beater and mocked him for using an inhaler during his last fight.

"I'm guessing he doesn't have that much oxygen in his head," Lewis said.

But, then he issued this challenge ...

"If he can get through Volkov, which I don't think he would, then for sure I would like to fight him next."

Derrick says he's 100% confident he'd smash Hardy in the Octagon and win by knockout.

But, first Lewis has a big fight at UFC 244 this weekend -- taking on Blagoy Ivanov, the #8 ranked heavyweight.