The wartime Bosnian Serb general was driving a hard bargain, insisting on financial security for his helpers and family and amnesty for those who sheltered him, Marko Nicovic told Mina, the Montenegrin news agency.
No one in the government was available for comment.
Belgrade is under intense pressure to hand over the remaining war crimes fugitives, including Mladic and his political leader Radovan Karadzic, or be halted on its path to join the European Union and Nato.
A peaceful surrender of Mladic is crucial for the government because if police or guards were hurt while arresting the former general it could affect the government's popularity, Mr Nicovic said.
"The topic of negotiations is certainly also what the general will say in The Hague," Nicovic said. Mladic knew all about the former Yugoslav army's involvement in the Balkan wars, he said.
The report comes days after Serbia's war crimes prosecutor, Vladimir Vukcevic, said the authorities were on to a number of people who were in contact with suspects indicted for war crimes and warned them they would be criminally prosecuted if they continued to help runaways in any way.
Karadzic and Mladic have been charged with genocide for the 1995 Srebrenica massacre of 8,000 Muslims and the siege of Sarajevo, which claimed more than 10,000 lives during the 1992-95 war in Bosnia.
Serbia's Interior Minister, Dragan Jocic, repeated on Friday that arresting the remaining fugitives was the priority of the police, as well as the state and military intelligence services.
Six indicted UN war crimes suspects are still at large, all of them Serbians or Bosnian Serbs, including Karadzic and Mladic.
Serbia delivered 13 war crimes suspects to the tribunal this year, the last one in April. Western officials have told Serbia they wanted to see more action and not just promises.