The Brazil playmaker has been strongly linked with a move back to his old club AC Milan after falling down the pecking order under Mourinho.
Madrid are seemingly keen to sign Croatia international Luka Modric from Tottenham before the close of the summer transfer window, and Kaka is deemed surplus to requirements.
And now Mourinho has disclosed that he is open to the idea of selling the 30-year-old is a suitable offer arrives.
“If Kaka stays I would be happy and I am happy if he wants to go. In football it is normal that the players play where they want,” the Portuguese told AS.
“He is a very good footballer and prepared to be at his maximum level. If he decides to stay, then perfect.
“If he goes, that’s perfect too but we are not going to give him away for free. Those that want him have to pay for him.”