Mundine, father of Williams' trainer Anthony Mundine, said he should think long and hard about making boxing his primary occupation following this year's Rugby World Cup.
"I said to (Williams) in 12 months time he could be the second Ali. He could be anything," Mundine said.
"I saw him about 12 months ago, I really thought he moved like Ali.
"He needs more fights ... If he keeps on boxing seriously, he will be the second Ali."
Oh yeah? Williams might be a reasonable rugby player, but as a boxer, he's not good enough to tie Ali's shoelaces; unless, of course, Mundine Snr was referring to Ali Williams, in which case he might have a point!