The next hearing is scheduled for 2 p.m. on Thursday, and the court will proceed with the trial regardless of whether Yoon is present or not, acting court President Moon Hyung-bae was quoted as saying by Yonhap news agency, citing the relevant law.

Yoon's failed martial law imposition bid had plunged South Korea into a deep crisis last month.

The hearing was held exactly a month after a National Assembly voted to impeach Yoon from his position.

Yoon's lawyers were quoted as saying by Yonhap earlier that the president, who has been suspended from his duties, will not attend the hearing due to concerns about his personal safety amid investigators' attempt to detain him on charges of insurrection and abuse of power related to his martial law decree.

Moon said the court decided to dismiss Yoon's request to exclude one of eight justices -- Chung Kye-sun -- from the trial.

The decision was unanimous among the seven other justices, he said.

Yoon's lawyers demanded Chung's exclusion by citing concern that her past work as the leader of a progressive law research society could undermine the chances of a fair ruling.

"It is regrettable that our request was dismissed for no particular reason," Yun Gap-geun, a lawyer for Yoon, told reporters after the hearing as quoted by Yonhap.

"I believe a justice with common sense will recuse herself," the lawyer said.

The court now has 180 days to decide whether to uphold or reject Yoon's impeachment from the day it received the case on December 14.

If upheld then Yoon will be removed from his office, a move that can trigger snap polls within 60 days.

If dismissed then he will be reinstated.