One-Armed MMA Fighter -- Why Can't I Fight in the UFC? I'm Stumped!

MMA fighter Nick Newell might only have one arm ... but he's definitely got plenty of balls ... telling TMZ he's more than capable of fighting in the Octagon -- even if UFC prez Dana White isn't convinced he can pull it off.

Nick's already the undefeated belt holder in the Xtreme Fighting Championship, but tells us he'd kill to cross over to UFC -- however, White's expressed reservations because, as he puts it ... "It's hard to fight with two arms, you know what I mean?"

Nick's response to Dana is honestly, brutal -- "I've won by arm bar, rear naked choke, guillotine, heel hook, TKO and knockout. In 9 pro fights I have never been out struck."

He adds, "If you have followed this sport, or know anything about it, you would be able to see that I'm amongst its elite. Just because I'm not in the UFC doesn't mean I wouldn't beat most of the guys in there."

Your move Dana.