Karadzic, who is conducting his own defence, is facing 11 charges of genocide, war crimes and crimes against humanity in connection to the 1992-95 Bosnian war.
He has repeatedly refused to enter pleas, but insists he is innocent.
He has said he wants more time to review a million pages of prosecution evidence and the statements of hundreds of witnesses.
O-Gon Kwon, the presiding judge, has said that the court would consider imposing a lawyer to represent Karadzic if he continues to boycott the proceedings.
"I would like to repeat once again to Mr Karadzic our previous warnings ... should he maintain his position that he will not attend the trial we may proceed in his absence and assign counsel to represent him," the judge said on Monday.
"We advise him to consider this carefully prior to making his oral submissions tomorrow [Tuesday]."
Karadzic faces genocide charges over the Sarajevo siege and the massacre of Muslim men and boys at the UN-protected enclave of Srebrenica in July 1995, in which about 8,000 people died.
His trial is expected to last for up to two years and he faces a maximum sentence of life in jail if convicted.
Karadzic was arrested in Belgrade last July after 13 years on the run.
He had been posing as a New Age healer named Dr Dragan Dabic, and had disguised himself with thick glasses, a bushy beard and straggly grey hair.
Prosecutors had wanted to try Karadzic alongside his wartime military chief, General Ratko Mladic, but he has yet to be caught.