Proceedings in the trial against Sary have been adjourned until Wednesday. Sary has been undergoing emergency treatment for bronchitis since Thursday at the Khmer-Soviet Friendship Hospital, The Phnom Penh Post reported.
Sary's attorney, Michael Karnavas, said he is unsure Sary will be able to actively participate in proceedings at this time.
"My impression is that my client is probably best to have the week off and rest," Karnavas said. "With his present condition, we don't know yet how capable he is to follow proceedings. If he falls asleep in the holding cell, that's not active participation."
If Sary's condition deteriorates, Open Society Justice Initiative trial monitor Clair Duffy said he may need to be severed from proceedings.
Sary's wife, also on trial for crimes against humanity, has already been severed from proceedings.
The elderly former high-ranking official in the Pol Pot government is on trial for genocide for his involvement with the killings of nearly 2 million Vietnamese and Muslim minority group members in Cambodia, the BBC reported.