Independent Dutch tests on the body of Slobodan Milosevic show no signs that he was poisoned, the international war crimes tribunal in The Hague has said.
Supporters have filed past Mr Milosevic's body in Belgrade
The tests also found no trace of unprescribed drugs capable of causing his death, the head of the tribunal added, quoting provisional results.
The ex-Yugoslav president died of a heart attack at The Hague tribunal.
Supporters say he was poisoned - but others allege he took unprescribed medication on his own.
None of Mr Milosevic's immediate family members, most of whom now reside in Russia, will attend the funeral, the funeral's organisers have said.
The former leader had asked to be treated in Russia and it was alleged he took unprescribed medicines to boost his case.
The tribunal, which had been holding him since 2001 on suspicion of committing war crimes in the Balkans in the 1990s, rejected the plea.
The toxicological tests were carried out by the Netherlands Forensic Institute in The Hague.
"So far no indications of poisoning have been found," Judge Fausto Pocar, president of the Hague tribunal read from the report.
He said the Dutch team had found no traces of rifampicin, a powerful antibiotic that could have counteracted Mr Milosevic's medication for his heart condition.
This meant only that the antibiotic had not been "ingested or administered in the last few days before death", the report said.
Questions were raised about the cause of Mr Milosevic's heart attack after a Dutch expert said traces of rifampicin had been found in his blood in recent months.
Mr Pocar added that other drugs were found in the samples tested but "not in toxic quantities".
Mr Milosevic reportedly said he feared he was being poisoned just a day before his death while other reports suggest he knowingly took harmful medicines to boost his case for going to Russia.
Branko Rakic, the late defendant's legal adviser, said the tribunal was "panicking and trying to whitewash" its denial of his request to be treated in Russia.
SATURDAY'S FUNERAL SCHEDULE
Farewell ceremony outside parliament
Departure for home town of Pozarevac
1300 GMT: Public viewing at Pozarevac City Hall
1400 GMT: Burial in grounds of family home
"We cannot say he was murdered but certain omissions have been made and as a result, he died," he said on Friday.
"If Milosevic had been in a hospital, he would have been alive today."
Tribunal officials on Friday said they were aware that Mr Milosevic had been taking unprescribed medicine as far back as 2004.
But they denied that they acted irresponsibly, saying they continued to monitor the former president.
An external investigation into the running of the UN jail was also announced.
Mr Milosevic died last Saturday in his cell in The Hague, aged 64, and will be buried in Pozarevac, eastern Serbia, on Saturday.
His funeral is being organised by his Socialist Party, which confirmed on Friday that he would be buried in the absence of his family.
"It is now definite the family will not be coming to the funeral," Milorad Vucelic, deputy party president, told Serbian state television.
His widow Mira Markovic, his son Marko and his elder brother Borislav are based in Moscow. His daughter Marija still lives in Montenegro.
A few thousand people have paid their respects to Mr Milosevic's coffin, which has been on display at a Belgrade museum since Thursday.
However, most people in Serbia have greeted Mr Milosevic's death with a resolute indifference, the BBC's Allan Little in Belgrade reports.