The 48-year-old did not appear for a routine call-over hearing at the Westminster Magistrates’ Court in London on Monday.
Assange is fighting extradition to the U.S. to face 17 charges of violating the U.S. Espionage Act and one of conspiring to commit computer intrusion.
The U.S. Department of Justice made fresh allegations last week that Assange recruited hackers at conferences in Europe and Asia to provide WikiLeaks with classified information, including military secrets.
Judge Vanessa Baraitser said she had received an email about the superceding indictment, but defence lawyers were annoyed.
Prosecution barrister Joel Smith said both parties were still considering the impact of the superceding indictment.
“If we need to involve the court … then we will inform the court at the appropriate time,” he said.
Barrister Mark Summers said via telephone that the defence only heard about the new indictment against Assange from media reports.
“We were surprised to hear about it in the media,” he told the court.
Summers said the fresh allegations could impact the upcoming case management hearings.
The defence is due to provide the court with its final evidence on July 10.
Assange did not to attend due to the coronavirus risk and hasn’t been seen in court for about three months.
Smith said that the prosecution’s psychologist hadn’t been able to assess Assange in prison due to the coronavirus lockdown.
Judge Baraitser said Belmarsh prison officials had emailed her to say that he was not unwell, he was refusing to attend.
The judge said Assange could only be absent if he was actually unwell, not if he was worried about becoming ill.
She said if he did not attend the next call-over on July 27 he would have to provide a medical certificate.
Summers said that the defence could do that if required.
The Australian is accused of publishing thousands of secret U.S. diplomatic and military files, some of which revealed alleged war crimes in Iraq and Afghanistan.
He’s also accused of trying to recruit hackers to provide WikiLeaks with classified U.S. information.
The charges carry a total of 175 years’ imprisonment.