Mr Assange took refuge in London’s Ecuadorian embassy in 2012 to avoid extradition to Sweden over sex assault claims, which he denies.
He earlier tweeted he would accept arrest if the panel ruled against him, but if the decision went his way the arrest warrant should be dropped.
The Met Police said he will still be held if he does leave the embassy.
A warrant for his arrest remains in place.
In 2014, Mr Assange complained to the UN that he was being “arbitrarily detained” as he could not leave the embassy without being arrested.
The UN’s Working Group on Arbitrary Detention is due to announce the findings of its investigation into the case on Friday.
Its panel of legal experts, which has taken evidence from the UK and Sweden, has made previous rulings on whether imprisonment or detention islawful.
It does not have any formal influence over the British and Swedish authorities and the UK Foreign Office said it still had an obligation to extradite Mr Assange.