AC Milan vice-president Adriano Galliani has reiterated his desire for the club to re-sign Kaka from Real Madrid, but admitted the financial issue could be a stumbling block.
Kaka, 30, has struggled for consistency at the Spanish champions since he left the San Siro for £50.7 million in 2009.
The Brazil playmaker was on the sidelines as Los Merengues beat Real Oviedo 5-1 in a pre-season friendly on Tuesday and, having also failed to make the squad for a tour of the United States, speculation is rife over his long-term future.
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 Primera Division goals last term as Jose Mourinho's side wrested the championship from Barcelona.
On Thursday, the player's representative in Italy confirmed talks were underway.
"Yes, we are talking about him," Gaetano Paolillo told Sky Sport Italia. "But I can't add further information at the moment."
Rumours of the Brazilian's arrival stepped up a notch on Thursday morning, with the announcement that AC Milan had not named a No. 22 for the coming season, meaning that the Brazilian's former shirt number has been kept available.
The potential arrival of Kaka was greeted positively by Milan fans, who have suffered the loss of Thiago Silva and Zlatan Ibrahimovic in recent weeks.
Former striker Filippo Inzaghi, who this week returned to the club as a youth coach, summed up feelings in among supporters, saying: "As a Milanista, his possible return gives me goosebumps."