The 23-year-old says that the return of the Brazilian can help the Rossoneri reassert themselves as the dominant force in Italy
The Brazil international rejoined the club on a free on transfer deadline day after leaving the Rossoneri for Real Madrid in a €65 million deal four years ago.
Milan endured a terrible start to last season but a revival saw them finish in third spot and Poli - another of the club's summer additions - believes the 31-year-old can be the catalyst behind a resurgence this term.
"He is an extraordinary footballer and I am very happy he has returned," he told the club's official website. "He has come back very hungry and I'm sure he will achieve great things here.
"It is a great privilege to be playing with him and he will be our leader."
Meanwhile, defender Philippe Mexes echoed his team-mate sentiments and backed Kaka to act as a mentor for the club's younger attacking talents.
"I think we have all the qualities to show that we can be competitive," the Frenchman added.
"Kaka is a great player and will help the attackers like [Mario] Balotelli and [Alessandro] Matri."
Milan travel to Torino in Serie A on Saturday.