Milan were forced to sell big-name players such as Zlatan Ibrahimovic and Thiago Silva to Paris St Germain this summer, but Galliani insists that trend will have to continue.
An abysmal start to the domestic campaign sees the Rossoneri sit ninth in Serie A and, despite an encouraging 1-0 victory over leaders Juventus, they sit 14 points adrift of top spot.
The seven-time European champions lost the spine of their squad over the summer but have still managed to qualify for the knockout stages of the Champions League.
"I suffered a lot from the sale of Ibrahimovic but the economic situation in this country is what it is," Galliani told www.acmilan.it.
"Ibra was a great player but a luxury we could no longer afford."
It is not all doom and gloom at the San Siro as the departure of Ibrahimovic has allowed young forward Stephan El Shaarawy to excel, scoring 10 league goals already this season.
"With Ibra in the side El Shaarawy may not have scored so many goals," added Galliani.
As the January window approaches, CEO Galliani has stated that Milan, owned by former Italy Prime Minister Silvio Berlusconi, are firmly in the selling market.
He explained: "We have 23-30 players. First we must sell then we can buy, when we have reduced the squad size.
"We have some players who want to leave, not many, and others who we had already sold but didn't accept the offers because they like it here at Milan.
"I have to thank president Berlusconi because for the last 26 years he has allowed Milan to eat and drink caviar and champagne."