Matt Canavan could be in political limbo for at least six months while the High Court determines if he should be forced out of Parliament.

Key points: High Court asked to decide on Matt Canavan's citizenship circumstances

High Court asked to decide on Matt Canavan's citizenship circumstances Greens leader Richard Di Natale calls on Senator Canavan to resign

Greens leader Richard Di Natale calls on Senator Canavan to resign "It's a bit like the dog ate my homework, isn't it?" Cory Bernardi says

Senator Canavan quit Cabinet on Tuesday after discovering he was an Italian citizen, which made him ineligible to stay in Parliament.

But he will hold on to his Senate position while he asks the High Court to decide on his extraordinary circumstances.

Senator Canavan said he did not know his mother's decision to take Italian citizenship included him and he said he did not authorise it.

So he intends to remain in the Senate while he fights in the High Court.

But Greens leader Richard Di Natale has called on Senator Canavan to resign immediately.

Greens Larissa Waters and Scott Ludlam resigned as senators when they discovered they had dual citizenship.

Senator Di Natale said his colleagues had taken responsibility for their own actions.

"Now Senator Canavan should do the right thing by the Australian people too and resign immediately," he said.

University of Sydney constitutional expert Anne Twomey said the High Court would try to deal with the case quickly, but it could still take months to make a ruling.

"I suspect the High Court would be prepared to expedite the case because of the importance of the Senate and the balance of power in the Senate, but even then you've got to wait for the parties to find all the relevant evidence," Professor Twomey said.

"It might be quite tricky working out Italian law and those sorts of things so the parties have to be ready to present their cases and the court has to be given a reasonable time to decide.

"At a minimum, I think probably six months."

The Government will ask the Senate to refer Senator Canavan's eligibility to the High Court when the Upper House next meets in just under two weeks.

Sorry, this video has expired Canavan family had citizenship discussion in 2005: Joyce

It's the 'dog ate my homework' excuse

Senator Canavan's former colleague Cory Bernardi, who now heads the Australian Conservatives, was sceptical that Senator Canavan would not have known about the Italian citizenship.

"Well, because it's a bit like the dog ate my homework, isn't it?" Senator Bernardi said.

"My father was Italian. We enquired into these citizenship matters many, many years ago and we found it was simply impossible to do as an adult, unless you were part of it yourself."

But Liberal senator Simon Birmingham said that was the basis of Senator Canavan's argument to the High Court — that the Italian citizenship might not be valid because he did not sign anything or take any steps himself.

Queensland Federal MP Bob Katter dismissed Senator Canavan's claim he did not know about the dual citizenship.

"If you're telling me someone was made a citizen of another country without your knowledge, you'd be seriously testing my intelligence. I mean, give me a break!" Mr Katter said.

"Ignorance of the law has never been an excuse and I don't think that any jury or court in Australia — or the public — would be so gullible to believe you could be unaware you'd been made a citizen of another country.

"There is no jury or court that would be that gullible to believe that. They might be prejudiced to make that decision, but not gullible enough to believe that his mummy made him a citizen of Italy without him knowing."