Adriano Galliani has admitted Kaka would have to agree to a considerable pay cut if AC Milan were to have any chance of bringing him back to the San Siro.
The Brazilian enjoyed a hugely successful spell with Milan before leaving to join Real Madrid in a big-money deal in the summer of 2009.
His progress at Real has been hampered by injuries and speculation has suggested he could be set to move on again this summer.
Milan vice-president Galliani has previously insisted there are no plans in place to try and sign the 28-year-old, and he believes a deal would be difficult to finalise.
"Kaka's return to Milan? Ricardo earns too much, because in Spain they pay less taxes," Galliani told RaiDue.
"I am sorry that he has problems in Madrid, but to come back to us he would have to drop a lot his salary.
"We can afford the wage of only one (player like) Ibrahimovic."
Milan supremo Silvio Berlusconi agrees that it would be hard to re-sign Kaka but concedes it would be great to have him back.
"Kaka? Should he want to come back, it would be good news," Berlusconi told Tuttosport.
"Anyway, I don't think it is possible, not at this moment.
"But should he want to come back, this would really be great news for Milan and for all supporters."
Galliani also reiterated Milan's position on Roma defender Philippe Mexes, who is reportedly a target for several clubs as he approaches the end of his current deal.
"Philippe Mexes to AC Milan? He is followed by half of Europe," said Galliani.
"There is not only us after him. But now we're not going to disturb him at this time of the season."