Just an extension on what Deathkiss said, when Fredo and Mike are first introduced to Johnny Ola in Cuba. Fredo and Johnny Ola are personally introduced and I think it was asked of Fredo if he had met Ola before and Fredo says no, they shake hands in introduction and Fredo gives a really great awkward glance to Ola (as in awkward first introduction).

Later when Fredo takes Mike's and Roth's enterage out for the evening for entertainment, particularly that weird erotic cuban club, it's asked of Fredo or Fredo foolishly elaborates to the fact that Johnny (Ola) told him about this place. Johnny knows all the best places. This shows Mike that is was Fredo who had prior connection to Ola.