"I think it's best to leave the August controversies behind because they will pass with time just like football matches," Ranieri told the Corriere dello Sport.
"However, Mourinho has shown everyone what he is really like by unveiling his true personality and what he thinks of his colleagues.
"It will be very difficult for him though. He has taken charge of a team that has won two consecutive titles and he will be expected to win everything.
"But I have gained a certain wisdom from my 70 years and I will be the first to congratulate him if he succeeds."