Julian Assange was too sick to appear at an extradition hearing Thursday, his lawyer said in court.

Attorney Gareth Pierce said the WikiLeaks founder was “not very well” and couldn’t appear via video link from prison.

Assange, 47, has been behind bars at Belmarsh Prison in London serving a 50-week sentence for bail jumping in Britain.

He is fighting extradition to the US, where he is charged with conspiring with former Army intelligence analyst Chelsea Manning to illegally obtain and disclose classified information, and is under criminal investigation in Sweden on rape allegations dating back to 2010.

On Wednesday, WikiLeaks said it has “grave concerns” about Assange’s health.

“During the seven weeks in Belmarsh his health as continued to deteriorate and he has dramatically lost weight,” WikiLeaks tweeted. “The decision of prison authorities to move him to the health ward speaks for itself.”

The Australian whistleblower was arrested in April after spending seven years holed up inside the Ecuadorian embassy under political asylum — to avoid being sent to Sweden in the rape case.

A new date for the extradition hearing was set for June 12 and it may be held at Belmarsh for convenience.

“It may be more convenient for everyone if it’s there,” said Westminster Chief Magistrate Emma Arbuthnot.

Sweden could also file an extradition request. A UK judge will likely decide which country gets first crack at trying Assange.

With Post wires