The attorneys representing Saddam and seven co-accused on charges of crimes against humanity, considered a second day of hearings set for 28 November to be "cancelled and illegitimate", lead counsel Khalil al-Dulaimi said on Wednesday.
The judge said the court was considering its response.
But the Iraqi prime minister made clear he would not heed calls to move the trial abroad. Hinting Saddam's own followers had a hand in the killings, he said lawyers had refused police protection.
Al-Dulaimi said he felt personally threatened. "We're facing daily threats," he said after the defence team issued a statement blaming the US-led forces and the government for failing to provide security for them.
Al-Dulaimi renewed demands for the United Nations to halt the trial after Tuesday's killing of Adil al-Zubeidi, who defended Saddam's half-brother Barzan and the former vice-president.
Judge Rizgar Amin, who presides over a panel of five trial judges, said they had yet to decide how to respond to the problem: "Now is the time to sit and talk and discuss this among ourselves so we can reach a decision in the coming days."
It was for the government to protect the lawyers, he said.
Prime Minister Ibrahim al-Jaafari said the lawyers had turned down an offer of protection from the Interior Ministry. The killers of Saadoun al-Janabi, counsel for another co-defendant, told witnesses they were from that ministry before abducting and shooting him the day after the trial opened on 19 October.
"I hope they will cooperate with us now," al-Jaafari told reporters. He said Saddam supporters were exploiting the deaths: "If you seek the cause...seek him who benefits," he added.
It was unclear what effect a defence boycott would have on the tribunal, which has the power to appoint counsel. However it would clearly dent efforts by the Iraqi and US governments to show that the trial is entirely fair.
Legal sources said that a failure of defence counsel to appear on an appointed date would normally cause an adjournment.
Al-Zubeidi was buried on Wednesday, virtually in secret, police said, by relatives afraid of an attack on any funeral ceremony.
Gunmen shot al-Zubeidi in his car in Baghdad. Thamer Hamoud al-Khuzaie, a fellow member of the defence team, was wounded.