Julian Assange was too ill to appear at his London hearing on Thursday, his lawyer said.
WikiLeaks founder, 47, is struggling to be extradited to the United States over prosecution related to American secret secrets.
He should have appeared in his trial hearing via video connection from Belmarsh Prison, but lawyer Gareth Peirce said he was "not very good".
According to WikiLeaks, Assange moved to prison in prison
A spokesman for the whistleblowing website said it had "serious concerns" about Assange's health.
"In the seven weeks in Belmarsh his health has continued to deteriorate and he has dramatically lost," said the spokesman.
"Defense lawyer for Assange, Per Samuelson, said that Julian Assange's health condition on Friday was such that it was not possible to make a normal conversation with him."
The five-minute hearing on Thursday in Westminster Magistrates & # 39; Court was the second in Australia's extradition case.
The US Department of Justice has ordered Assange to receive and publish thousands of classified documents in connection with the wars in Iraq and Afghanistan
The United States wants the United Kingdom to extradite him, but Assange has formally rejected consent.
On Thursday, Chief Executive Officer Emma Arbuthnot set the next hearing on June 1
Supporters of Assange queued outside the courthouse for more than an hour to enter the public gallery.
Outside court, some sang:" Free Julian Assange. "
Assange sought political asylum in the Ecuadorian embassy in London in 2012. He currently serves a 50-week sentence in the Belmarsh prison in southeast London for citizen violations.
Earlier this month Swedish prosecutors reopened their investigation into rape attacks against Assange, which he refuses.