The Brazilian is beginning to return to his best after his summer arrival from Real Madrid.
"Kaka arrived and then immediately had an injury," said Montolivo, who like Kaka scored in the 3-1 win at Catania on Sunday.
"But he's a great champion and he makes the difference in every match. He brings with him lots of experience.
"Let's hope he keeps it up and he's got great charisma."
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