Alleged war criminal Charles Zentai has had a stroke on the eve of a new court battle to send him to Hungary to face claims he murdered a Jewish teenager during World War II.

The Federal Government has already spent at least $455,000 on its campaign to extradite the 89-year-old with the costs of the latest appeal yet to be revealed.

Today in Perth, three interstate Federal Court judges will start hearing a Commonwealth appeal against Federal Court Justice Neil McKerracher's ruling last July that the Government made an "error of law" in agreeing to extradite him.

Mr Zentai is at home in Willetton after being rushed to hospital on Friday following the minor stroke which caused him to lose his speech temporarily.

His son Ernie Steiner said his father would not be at court today.

In response to a Senate question in March, Home Affairs and Justice Minister Brendan O'Connor confirmed the Federal legal bill so far was $455,000 - $247,000 of it for defending Mr Zentai's challenges to the extradition process.

But the figure is sure to be significantly higher now with the cost of the latest appeal not revealed.

In March, Mr O'Connor said it would be inappropriate to estimate the cost of the current appeal, but it was the right course of action.

He said Justice McKerracher's decision raised "significant and complex issues" for the administration of the extradition scheme.

Mr Zentai denies involvement in the murder of the teenager when he was in the German-aligned Hungarian army. Justice McKerracher granted a stay of the extradition warrant granted by Mr O'Connor, ruling the minister's order was beyond his jurisdiction, the war crime was not an extraditable offence and there was a failure to consider Mr Zentai's advanced age, ill-health and the "severity of the sentence in the circumstances".

The Government argues Justice McKerracher erred in his findings that Mr O'Connor had no jurisdiction and that Mr Zentai was not eligible under the Extradition Act.

Mr Steiner said his father had a history of "mini-strokes" and believed stress of the new appeal triggered his latest episode.

He fears his father's extradition would be a death sentence.

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