"Let the best man win," Prokhorov said, joking about his competition with Cuban to sign Williams. "If he wins, I will crush him in a kickboxing throwdown."
The 6-foot-9 Prokhorov has a significant reach advantage over Cuban, but it wouldn't be Cuban's first brawl with a much bigger foe.
"He obviously didn't see me be the first in WWE history to put Sheamus on the mat," Cuban replied Wednesday night via email, referring to his guest host appearance on "Monday Night Raw" in 2009. "He knows not what he gets himself into."