Galliani returned to Milan on Wednesday night after spending the last two days in Paris locked in talks with PSG executives regarding the possible sale of the Brazil defender to the Ligue 1 side.
"(AC Milan owner Silvio) Berlusconi intends to resist all offers from PSG for Thiago Silva," Galliani said to Sky Italia.
The 27-year-old Silva is also a reported target of Manchester City, Chelsea and Barcelona.
The French giants recently increased their bid to 50million euros to acquire Silva, who is under contract with the Serie A outfit until June 2016.
PSG sporting director Leonardo, who coached AC Milan in the 2009-10 campaign, said to Sky Italia: "There is no agreement.
"Many details have not been defined but this is normal considering the type of deal we are talking about.
"We will wait and see but I don't think the negotiations will take very long."
Silva joined AC Milan in December 2008 from Fluminense in a deal worth under 10million euros.
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