LeBanner destroyed Hunt in Paris. Hurt him pretty bad, but didn't KO him. At this point I don't think there is anyone in the circuit that can KO him w/ a single punch/kick. Not even Cro-Cop.
If the Tyson of 10 years ago landed a picture perfect right hand to the point of Hunt's chin, with an MMA glove, that might stop him.
No one.
Speaking just MMA, Roman Zentsov might be able to drop Hunt and hurt him (I doubt we will ever see Hunt hit and KOed in this lifetime)
He KO'ed Pedro Rizzo with on perfect left hook, KO'ed Yvel with a short left hook while walking backward, and hurt and dropped Dirty Bob Schreiber, who was known as having a pretty hard head.
I don't really give him a big chance to, but he has put the lights out of some pretty good stand up fighters.