Board Thread:Versus Debates/@comment-31377172-20200228010635/@comment-32685487-20200301152732

Kisame knows his own abilities and he knows what he has seen of Itachi's abilities, he was confident Itachi was stronger than him and in the series when one person says that that means that the stronger person will defeat the weaker person in battle. Itachi already knows Kisame's abilities too so obviously Kisame's chakra absorbing abilities are something Itachi can defeat.