The board had previously ruled Mr Demjanjuk be sent to Germany to stand trial.
Even if doctors rule him fit, Mr Demjanjuk's trial may prove risky without being revelatory.
Prosecutors point to a re-interpretation of criminal law after the conviction of John Demjanjuk, in May 2011.
BBC: Former Auschwitz Nazi guard Hans Lipschis found in Germany
Prosecutors have pointed to a re-interpretation of criminal law after the conviction of John Demjanjuk in May 2011.
Mr Demjanjuk arrived in the US in 1952 as a refugee, settling in Cleveland, Ohio, where he worked in the car industry.
On Friday, Mr Demjanjuk, who lives in Cleveland, Ohio, was given a reprieve from deportation after arguing that his case should be reopened.
In 1993, the Israeli Supreme Court cleared John Demjanjuk of war crimes after hearing evidence that he was known as "Ivan the Terrible" at prison camps.
In March this year Ukrainian-born John Demjanjuk, found guilty for his role as a Nazi guard at the Sobibor death camp, died aged 91.
But Mr Demjanjuk, who came to the US in 1952, says he was a prisoner of war of the Nazis rather than a prison guard.
The chief prosecutor at Germany's office investigating Nazi war crimes, Kurt Schrimm, said details on the suspect came to light during the high-profile Demjanjuk investigation.
Wolfgang Benz, head of the Centre for Anti-Semitism Research at Berlin university, said the case was about establishing whether Mr Demjanjuk was guilty, not exacting punishment.
In 2002, a US immigration judge ruled that there was enough evidence to prove Mr Demjanjuk had been a guard at several Nazi death camps and stripped him of his citizenship.
Mr Demjanjuk returned to the US, but in 2002 had his US citizenship stripped because of his failure to disclose his work at Nazi camps when he first arrived as a refugee.
Mr Demjanjuk was charged on 13 July, 10 days after medical experts at Munich's Stadelheim prison declared that he was fit to stand trial, provided that his questioning in court was limited to two 90-minute sessions per day.
Even though the Demjanjuk conviction isn't considered legally binding because he died before his appeals were exhausted, the special German prosecutors' office that deals with Nazi crimes has said about 50 other people in the same category are being investigated.
But on Tuesday, court officials and Mr Demjanjuk's lawyers said the start of the trial had now been scheduled for the end of the month, and that the 35 trial days set aside would probably take until early May 2010 to complete.
But the case is now being pursued on the same legal theory used to prosecute former Ohio autoworker John Demjanjuk, who died last year while appealing his 2011 conviction in Germany for accessory to murder on the grounds that he served as a guard at the Sobibor death camp.
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