The High Court has been thrown a new curveball in the citizenship fiasco, with concerns about whether former Nationals senator Fiona Nash's replacement should get a six-year term in Federal Parliament.

Key points: Fiona Nash was given six-year Senate term at 2013 election

Fiona Nash was given six-year Senate term at 2013 election Jim Molan was seventh on Coalition ticket, behind Concetta Fierravanti-Wells and John Williams, both on three-year terms

Jim Molan was seventh on Coalition ticket, behind Concetta Fierravanti-Wells and John Williams, both on three-year terms Question is whether those two sitting senators should be moved up list and Molan placed at bottom

On the day many had expected Liberal candidate Jim Molan to be confirmed by the High Court as the new Coalition senator for New South Wales, it was revealed an independent lawyer had suggested he only get a three-year term.

There are no constitutional barriers for Mr Molan to take Ms Nash's spot in the red room.

Ms Nash, the former deputy Nationals leader, was kicked out of Parliament because of her dual citizenship.

Her post has remained vacant because the court refused to endorse Liberal Hollie Hughes after the first countback because she had held a government job after the election.

Mr Molan was the seventh candidate on the Liberals' and Nationals' joint ticket at the last election, and received more than 10,000 first-preference votes, almost double that of Ms Nash.

The 67-year-old was unhappy at being given the generally unelectable seventh spot on the Liberal and Nationals Senate ticket.

At a normal federal poll, only half of the Senate faces election.

Because the last election was a double dissolution, it was up to the Senate to decide which of its elected representatives received six-year or three-year terms — bringing the electoral cycle back in to line.

The standard practice is the top six elected senators in each state receive the longer term.

In the summons filed by the Government seeking the declaration Mr Molan be made a senator, it suggests he is filling the place for which Senator Nash was elected.

Ms Nash's seat was for a six-year term.

But documents filed to the court by Barrister Geoffrey Kennett SC suggest senators Concetta Fierravanti-Wells and John Williams should be moved up the list, and Mr Molan placed at the bottom where he would get a three-year term.

The court heard there were questions about whether the issue should be resolved by the High Court or the Senate, but Justice Stephen Gageler agreed the court should consider the matter.

Mr Molan told the ABC he never expected a six-year term anyway.

"I have no expectations, and I have no kind of feelings as to what the High Court should do," he said.

"It will work in its own manner, and at some stage I will be appointed as senator for New South Wales."

High Court to resume December 22 to decide next steps

Senator Fierravanti-Wells has already indicated she wants to be part of any future case.

Lawyers for Mr Molan have urged the case be resolved sooner rather than later.

The next hearing will be on December 22, at which time the arguments will likely either be dismissed or referred for consideration by the full bench of the High Court in the new year.

The outcome will also have an effect on the process to replace other senators dragged into the citizenship crisis, particularly the former Senate president Stephen Parry and independent Jacqui Lambie.

Both were given six-year terms.

The case seems unlikely to impact the tenure of Western Australian Greens senator Jordon Steele-John, who replaced colleague Scott Ludlam and picked up his six-year term.

Senator Steele-John has already been sworn in to the Upper House.

The lawyer who filed the summons, Mr Kennett was appointed by the High Court during the original seven citizenship cases to present alternative arguments to the bench.