Milan are in talks with Real Madrid about re-signing the Brazilian.
Maldini told TMW: "Kaka is young and can still do well. Of course, not everyone will be happy after the way he left. He did say he would not leave Milan.
"Now he is in difficulty, as is Milan. And that's why he might return, but from what I hear the biggest problem is the salary he has at Real Madrid. Milan cannot match it.
"The club two years ago has set a cap on salaries: they'll not ever give him the same money he takes in Spain."