Swedish lawyer Bjorn Hurtig says he plans to file the appeal Friday at Stockholm District Court.
Prosecutors claim attempts to question Assange have failed. Assange says his offers have been rejected.
Thursday's court order is troublesome for the globe-trotting Assange, whose current whereabouts are unknown, because it paves the way for Swedish prosecutors to seek his arrest abroad.
Assange is suspected of rape, sexual molestation and unlawful coercion related to encounters with two women in Sweden in August.
He denies the allegations.