Kaka joined Real from AC Milan in 2009, but has struggled to make a sustained impact at the Santiago Bernabeu and has been linked with a return to his former club.
Though the Brazilian is not a guaranteed starter for the Spanish champions, Mourinho is keeping an open mind regarding the playmaker’s future.
“I don’t know what will happen with his future and neither does he, but between us there are no doubts because he knows what I think and the market is open until August 31,” said Mourinho in Marca.
“Anything can happen. He could be a Real Madrid player next season and if he stays I would be delighted because we have a great relationship and he offers us things.”
Milan vice-president Adriano Galliani earlier reiterated his desire for the club to re-sign Kaka, but admitted the financial issue could be a stumbling block.
Quoted in Corriere dello Sport, he said: “There’s a long way to go with the negotiations. There are a thousand things that can scupper the deal, but great loves have the potential to surprise you.
“The important thing is that we’ve cast the first stone, but the ball is not in Milan’s court.
“The financial issue remains that the two systems are very different. Once a player leaves one country he can’t enjoy the same perks when he returns.
“We’re certainly interested. Kaka is a great player who has stayed in the hearts of all Milan fans. Let’s see. We’ll do what we can.”
He added in Gazzetta dello Sport: “We will do everything possible to bring him back to Milan, but we’re under no illusions.
“We need to be patient but at least I’ll be kept busy until the end of August.”