Berto's not just a premiere boxer (fighting Victor Ortiz in April) -- but he comes from an MMA family with his father, brother and SISTER all having competed in the Octagon.
So, when Berto told us he's been in contact with The Notorious ... we had to ask if he had advice for the UFC star.
Long story short ... Berto's not against a rematch with Diaz -- just not right now.
"I think that he should probably take another fight or two first," Berto said.
Check out the clip -- Berto's got some interesting advice for the Irish phenom.