Saquon Barkley's Uncle Challenges Deontay Wilder To Fight, I Bet I KO You!

58-year-old Iran Barkley -- Saquon Barkley's famous boxing uncle -- says he ain't done in the ring yet ... 'cause he's telling TMZ Sports he wants one last fight ... WITH DEONTAY WILDER!!

"I want to fight the heavyweight champ of the world," Iran says ... "I'm looking for that."

If you're unfamiliar ... Iran was actually a world champion boxer back in the day -- with 2 victories over Tommy Hearns and a near win over Roberto Duran on his 43-19-1 resume.

But, even though the guy hasn't fought since 1999 ... he says he ain't ready to hang up his gloves yet -- 'cause he wants one last fight with Wilder!!

Oh, and he says he'll win that, too, telling Wilder, "I bet I knock you out!!!"

By the way, Iran is Saquon's great-uncle, and Saquon's credited him in the past as a big reason why he's become one of the NFL's toughest running backs.

Which only means one thing ... better watch out for Saquon's high-school-aged little bro in a couple of years!!!