Hardy just agreed to fight the #7 ranked UFC heavyweight on Nov. 9 in Moscow -- replacing his training teammate Junior Dos Santos, who suffered an injury.

The former NFL star hasn't been beat in his pro career -- though he was DQ'd for an illegal knee against Allen Crowder ... and his victory over Ben Sosoli this past weekend was overturned because Greg used an inhaler between rounds.

Still, Hardy has been fairly dominant in the Octagon and when the opportunity came to fight a top-ranked opponent, the 30-year-old says he jumped at the chance.

"I'm excited, man," Hardy tells us ... "This is a a big-time fight, high-level competition. This is what any Prince of War or future King of War could ever hope for."

Hardy says he respects Volkov but believes he can knock out the Russian in under 3 rounds ... just like Derrick Lewis did in 2018.

"If 'Pillow Hands' Lewis can do it, I can go in there and compete," Hardy says.

Hardy says he plans to use this opportunity to show UFC fans he's the real deal.

"It's time to make a statement. It's time to step up and put my mettle to the test ... put my hands up and fight with an actual monster, fight with a top-ranked elite assassin."

We also spoke with Hardy about the inhaler controversy and he took full responsibility for the infraction -- vowing to make sure he's more educated on the rules for his next fight.

Hardy says he's not mad at his coaches and fight team for allowing him to use the inhaler -- saying they've done so much for him over the years, he can't get upset over one stupid mistake.

"This is the best team in the country, best team in the world ... two years ago I was a football player who couldn't throw a punch."