Greg Hardy says he's fired up to fight an "actual monster" in Alexander Volkov -- telling TMZ Sports, "It's time to make a statement."
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.