Australia's High Court has set down three days to decide on the citizenship of politicians, but the case might run three weeks.

Malcolm Turnbull's government could lose its one-seat majority if the court decides deputy Prime Minister Barnaby Joyce is in fact a New Zealand citizen.

Former Greens senator, Scott Ludlam could also find he resigned for no reason, if the court decides he isn't.

Sky's Kieran Gilbert told Mike Hosking the court is dealing with seven very complicated situations.

"Seven different cases and a real sort of constitutional analysis that needs to be done by the High Court. It could go for two to three weeks."

LISTEN ABOVE AS KIERAN GILBERT SPEAKS WITH MIKE HOSKING