Lawyers for 88-year-old alleged Nazi war criminal Charles Zentai are pursuing ways to prevent him being remanded in custody on Thursday.

Zentai lost a court appeal earlier this month to avoid extradition to Hungary on a charge of killing a Jewish teenager in Budapest in 1944.

Delivering its judgment that the former Hungarian soldier was eligible to be surrendered for extradition, the full bench of the Federal Court granted a stay of 14 days on the execution of the extradition warrant.

The stay lapses on Thursday, when Zentai is to be automatically remanded in custody as part of the legal process.

The Perth resident denies the Hungarian government's accusation that he was one of three men who tortured Peter Balazs in Budapest in November 1944, leading to his death.

He has fought against his extradition since a warrant was issued for his arrest in 2005.

Perth magistrate Barbara Lane last year ruled he was eligible to be surrendered for extradition to face the war crimes charge.

Zentai's lawyers appealed the decision in the Federal Court, but it was upheld by Justice John Gilmour in March.

The lawyers took the legal fight to the full bench of the Federal Court in August before the appeal was turned down on October 8.

Zentai has so far not taken up the option of applying to the High Court for leave to appeal.

Federal Attorney-General Robert McClelland has the final say on Zentai's extradition.

Mr Zentai's son, Ernie Steiner, on Tuesday said the attorney-general's department had written to the family's lawyers last week, saying it will not deal with submissions to keep Mr Zentai out of custody until court processes were finalised.

Mr Steiner said it was being argued this had happened immediately the courts ruled that his father was eligible for extradition.

He said an alternative avenue for his father to avoid custody was to seek a writ of mandamus in the High Court.

If issued, a writ of mandamus could compel the attorney-general's department to deal with the case.

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