Desire Munyaneza's trial was postponed Thursday after he was attacked Wednesday night.
"Someone attacked him last night and tried to kill him,'' his lawyer Laurence Cohen, said outside the courtroom where proceedings have halted until at least Monday.
"He was almost killed last night, so he has to be in the proper mental and physical state to stand trial.''
Cohen said 40-year-old Munyaneza was severely beaten and taken to hospital bleeding from his eyes and with possible head wounds. He has been transferred to another prison facility in Quebec.
"In jails, people get beaten up. I understand that,'' Cohen said. "The question is: Given the magnitude of this trial, the seriousness of the charges against Mr. Munyaneza, you would think that the authorities would be cognizant of all those issues.''
Munyaneza faces a life sentence on seven charges under Canada's new war crimes act, including genocide, crimes against humanity and war crimes.<
He faces a maximum sentence of life in prison if convicted, to be served in Canada.
The son of a wealthy Rwandan family, Munyaneza came to Canada in 1997 as a refugee and took up residence in Toronto, where he was arrested in 2005.
Munyaneza is accused of taking part in and ordering the rapes and killings during the genocide.
Estimates vary, but between 500,000 and 800,000 people, mainly minority Tutsis, were killed in 100 days of lawlessness.