By ESPNSTAR.com staff
The 30-year-old Brazilian has found it difficult to nail down a first team spot in Real Madrid since his move in 2009 after a series of injuries.
Kaka was on the sidelines as Real Madrid beat Real Oviedo 5-1 in a pre-season friendly on Tuesday and the fact that he also failed to make the squad for a tour of the United States has fuelled speculation over his future in the Spanish capital.
Speaking ahead of Madrid's friendly against Benfica in Lisbon on Friday evening, Mourinho told Marca: "Kaka will start tonight and play between 45 and 60 minutes.
"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.
"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."
The former Chelsea and Inter Milan boss was more definitive on Sahin's situation.
The Turkey international started only two La Liga games in his debut season last term and Mourinho claimed it would benefit him to go and play elsewhere - at least for a year on loan.
"I want to be honest and Sahin is living in this grey zone because the market is open," the Portuguese said. "If the possibility arises for him to go to another place it would be better for him to leave and to be able to have more minutes on the pitch."
However, Mourinho refused to be drawn on the possibility of Tottenham's Luka Modric coming in to replace either Kaka or Sahin, saying: "I will not speak about other clubs' players."
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.
Galliani hinted at his wish to see the player back with the Rossoneri earlier this week, but has now acknowledged "a thousand things" could make that impossible.
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."
Kaka, who was part of Milan's Champions League-winning side of 2007, scored 70 goals in six seasons with the Rossoneri.
But the former Ballon d'Or winner netted only five La Liga goals last term as Jose Mourinho's side wrested the championship from Barcelona.