Greg Hardy Boxing Hasim Rahman Jr. After Vitor Belfort Pulls Out W/ Illness

Hasim Rahman Jr. has found a new opponent ... former NFL star turned UFC fighter turned boxer Greg Hardy is stepping in last minute to save the main event after Vitor Belfort was forced to pull out after getting sick, it was announced Tuesday.

DAZN broke the news this morning ... announcing Rahman will square off against the ex-Panthers defensive end in just four days.

“I’m excited, man, this is my chance to show that I belong in the boxing world,” Hardy said.

“I know plenty about the Rahman name as boxers, and I know he was preparing for Vitor, but I’m definitely confident and prepared to show people I can box.”

Hasim and Vitor were originally set to go toe-to-toe on Nov.19 in Austin, TX ... but the bout was called off after the Brazilian mixed martial artist contracted COVID-19.

Rahman will have his hands full with Hardy ... who aside from being huge (Greg would have to cut to make the 265 lb. limit as a UFC fighter), also hits like a truck.

But, Hasim's also dangerous. The 31-year-old boxer -- whose dad was a heavyweight champ -- has a pro record of 12-1 (6 knockouts).

Of course, Rahman Jr.'s been one of the fighters feuding with Jake Paul of late. The men were scheduled to fight, but the bout fell apart weeks before. Hasim has been adamant the Problem Child's ducking him.