Ex-Bosnian Serb army chief Ratko Mladic, known as the "Butcher of Bosnia" was first hauled before the International Criminal Tribunal for the former Yugoslavia in The Hague on June 3, where he chose not to plead to what he called 11 "obnoxious" charges.
The court's regulations then gave Mladic a month before a second appearance where Dutch Judge Alphons Orie will again put the question to him.
"If he refuses, the judge will enter a plea of not guilty on his behalf," ICTY spokeswoman Nerma Jelacic told AFP on Friday.
Also at Mladic's second appearance, Judge Orie will have the chance to question Mladic on the conditions under which he is being held at a nearby UN detention centre and the preparations made by his defence team, Jelacic said.
"He has submitted a list of preferences which is under review," she added, with him represented by a court-appointed lawyer at his first appearance.
Mladic, 69, faced down ICTY judges following his arrest on May 26 in northeastern Serbia after 16 years on the run. Five days later one of Europe's most wanted men was transferred to The Hague by plane.
Once a strapping general in combat fatigues, a visibly older Mladic dressed in civilian clothes, told the court he was "gravely ill" and needed time to study the "monstrous words" in the indictment before entering a plea.
But his own words were no less defiant.
"I am General Ratko Mladic," he told the three-judge bench. "I defended my country and my people," he said after giving judges a left-handed salute.
Accused of committing atrocities during Bosnia's 92-95 war that killed 100,000 people, Mladic faces charges of masterminding the Srebrenica massacre -- Europe's worst mass killing since World War II -- and the 44-month siege of the capital Sarajevo from May 1992 in which 10,000 died.
His lawyers previously said he was treated for cancer two years ago while evading arrest and they also claimed he had suffered three strokes and two heart attacks, but ICTY officials said there was currently no indication that his health would impact the trial.
It could, however, take months to get under way and is likely to last for several years.
Mladic's one-time mentor Slobodan Milosevic died in The Hague four years into his own genocide trial in 2006 after a heart attack.
His former political chief, Radovan Karadzic has been conducting his own defence in his war crimes trial that started in October 2009.
Both Mladic and Karadzic face a maximum sentence of life in prison.