The Rossoneri chief is not optimistic about his side's chances of securing a return for the Brazilian and conceded the club cannot match the player's wages at the Santiago Bernabeu
The Brazilian playmaker has frequently been linked with a return to San Siro after struggling for fitness and form at Madrid following a €68 million transfer in 2009.
Earlier in the week, Kaka's agent confirmed that he was in talks with the Rossoneri about a summer swoop, but according to the club's vice-president, the tax system in Italy may prevent the deal from happening.
"It will be very difficult," Galliani told reporters after the presentation of the Serie A calendar for 2012-13. "There are a thousand factors which could make this impossible.
"As always, the problem is money. Milan cannot afford to pay some wages, because Spain have a different tax system.
"The law there has changed but only for future contracts. The contracts that were already signed will stay as they were."
Earlier on Thursday, the Italian giants dropped a strong hint that Kaka was on his way back to northern Italy by leaving the team's No.22 shirt unassigned.
"That shirt is free for the moment," Galliani noted.
Meanwhile, fresh reports in Italy suggest that Milan are interested in signing Kaka on a season-long loan to avoid paying a transfer fee for the 30-year-old midfielder.