Ratko Mladic's lawyer says he has a document proving the war crimes suspect has been battling cancer and that he was treated at a Serbian hospital in 2009.
Milos Saljic said Mladic has suffered from lymph node cancer and that he underwent surgery and chemotherapy for it in 2009.
The lawyer showed what he called a photocopy of a doctors' diagnosis saying that Mladic was in a Serbia hospital between April 20 and July 18, 2009.
The document has blackened out letterhead and signatures to hide the names of the hospital and the doctors who allegedly treated Mladic.
Serbia handed over the wartime Bosnian Serb army commander to the UN war crimes tribunal in the Hague, Netherlands, on Tuesday after he spent 16 years on the run.
The tribunal assigned a Serbian lawyer on Thursday to defend the former Bosnian Serb military chief when he appears before UN judges for the first time to face 11 war crimes charges.
Tribunal spokeswoman Nerma Jelacic said Aleksandar Aleksic has only been appointed for the hearing on Friday and that Mladic will likely indicate in court how he wants to organise his defence. Many high-ranking Serb suspects have defended themselves at the court, but Mladic's family has said he is in poor mental and physical condition.
At Friday's hearing, a judge will first ask Mladic to confirm his identity, if he understands the 11 charges against him and if he wants to enter pleas.
Serbia extradited Mladic to the court on Tuesday, five days after arresting him and ending his long flight from international justice. Saljic had argued that Mladic should not be extradited because of his ill health.
Mladic evaded capture despite his long-held status as Europe's most-wanted fugitive, charged with orchestrating Serb atrocities throughout the 1992-95 Bosnian war that left 100,000 dead and forced 1.8 million from their homes.