The Brazilian was considered at the peak of his powers when he joined Los Blancos at 27 but the veteran defender says the attacking midfielder has developed in the interim
The Brazilian was 27 when he arrived in the Spanish capital for a then world-record fee of €70 million but his time at the Santiago Bernabeu was blighted by injuries and poor form.
Indeed, there were those that questioned the wisdom of Milan's decision to re-sign the attacking midfielder on a free transfer this summer, particularly when he broke down again just after rejoining the Rossoneri, but Bonera says Kaka's performances in recent weeks have merely served to underline that he has actually developed as a player.
"He is appreciated by all of us," the 32-year-old defender told Corriere dello Sport. "He has improved in relation to his first spell at Milan.
"Ricky trained eight hours a day to recover from the injury [he picked up just after returning to Milan], without any complaints and making himself available to everyone.
"The fans see themselves in him. He's a good person, he gives his all, he sacrificed himself to return to Milan [by taking a wage cut] and it shows."
Bonera also voiced his support for Milan coach Massimiliano Allegri, who has come under pressure on account of the club's underwhelming start to the Serie A season.
"Personally, I have to thank him for a lot," the centre-half explained. "He is a good person as well as a good coach.
"He's always very serene. He analyses the situation calmly, but also knows how to raise his voice."