The Brazilian says that the thigh injury suffered by his compatriot has been a key factor to the Rossoneri's disappointing form of late
Massimiliano Allegri's men sit ninth in the table after six games, with Kaka having managed just one appearance since arrivng from Real Madrid last month.
And Robinho believes that Milan could have enjoyed a better start to their campaign had his countryman not picked up a thigh injury immediately following his return to San Siro.
"Kaka is a personal friend to me. He's a great player, I hope he can come back as soon as possible," Robinho told La Gazzetta dello Sport.
"We miss his quality so much; he is a decisive player."
Milan face champions Juventus on Sunday but will also have to do so without striker Mario Balotelli through suspension, after the forward's red card in the defeat to Napoli last month.
The Italy international has three goals and two assists to his name in Serie A already this season and Robinho says he will be missed.
"He is a champion; he makes all the difference," Robinho added. "He's a very strong personality on the field; he's very special."