Defense attorney Victor Koppe said Nuon Chea, 86, had not said whether he waived his right to be present during the proceedings.
The prosecution agreed to adjourn, The Phnom Penh Post reported
The Post said a hearing in March will determine Nuon Chea's ability to stand trial.
Co-defendant Ieng Sary, also accused of war crimes, is also suffering health problems.
At the beginning of proceedings, the Trial Chamber elected to try each senior leader of the Communist Party separately, as they weren't sure the men could stand a lengthy trial, The Phnom Penh Post reported.