Former Bosnian Serb army chief Ratko Mladic has filed an appeal against his extradition to the UN war crimes tribunal in The Hague.
His family says Gen Mladic is too sick to travel, but the Serbian government is expected to reject the appeal.
Gen Mladic is accused of committing war crimes during the Bosnian war, including the 1995 Srebrenica massacre of 7,500 Muslim men and boys.
Gen Mladic was seized last Thursday in Lazarevo village, north of Belgrade.
On Sunday, thousands of people rallied in Belgrade against his arrest.
The demonstrators hailed the general as a Serbian national hero. About 100 people were arrested during clashes with police in the Serbian capital.
Gen Mladic's lawyer, Milos Saljic, confirmed he had posted the appeal papers to Serbia's war crimes court from a postbox in Belgrade.
The court should receive the appeal on Tuesday and can then review it.
Serbian prosecutors labelled the move a delaying tactic.
Despite a decision by a Belgrade court that Gen Mladic was fit enough to be handed over to the UN court, Mr Saljic said he would request another independent medical examination, saying his client's health had deteriorated since his arrest.
"I don't think the trial will take place. He will not live to the start of the trial," said Mr Saljic.
It could take up to three days for the ministry of justice to decide on the appeal, but the BBC's Mark Lowen in Belgrade says it is likely to be rejected earlier, with Serbia's deputy war crimes prosecutor already dismissing the claim of ill-health as a delaying tactic.
"My impression is that he is acting in a very composed manner," said the prosecutor, Bruno Vekaric.
"As far as his mental state is concerned, believe me, he looks more normal than many others."
He also dismissed as ungrounded media reports that Gen Mladic had hearing difficulties and that his right arm was paralysed - possibly as a result of a stroke.
The government will hope Gen Mladic's departure will quell any further demonstrations by his supporters, adds our correspondent.
The Hague tribunal says it will not specify on which day Gen Mladic will arrive, but our correspondent says there is speculation he could be sent on a night-time flight, without prior warning.
Sunday's protests saw some 7,000 supporters of Gen Mladic rallying in central Belgrade to hear speeches from nationalist politicians and decry Mr Mladic's arrest.
Some in Serbia consider Gen Mladic a hero and resent the pro-Western government of President Boris Tadic for arresting him and planning to turn him over to The Hague.
Gen Mladic's arrest is considered crucial to Serbia's bid to join the European Union.
He evaded capture for 16 years after the end of the Bosnian conflict - just one of the ethnic wars unleashed in the 1990s by the break up of Yugoslavia.
On Sunday, Gen Mladic's son, Darko, said that despite the tribunal's indictment, his father had told him he was not responsible for the killings in Srebrenica, committed after his troops overran the town.
"He said that whatever was done in Srebrenica, he had nothing to do with it," he told journalists, after visiting his father.
Gen Mladic was seized early last Thursday morning Lazarevo, about 80km (50 miles) north of the capital.
Following the arrest of Radovan Karadzic in 2008, Gen Mladic had become the most prominent Bosnian war crimes suspect still at large.
He was indicted by the UN war crimes tribunal in The Hague in 1995 for genocide over the killings that July at Srebrenica - the worst single atrocity in Europe since World War II - and other alleged crimes.
Having lived freely in the Serbian capital, Belgrade, he disappeared after the arrest of former Yugoslav President Slobodan Milosevic in 2001.
President Tadic has said the arrest brought the country and the region closer to reconciliation, and opened the doors to EU membership for Serbia.