Former One Nation turned independent WA senator Rod Culleton has lost his spot in the Senate, following a bankruptcy decision.

Key points: Senate President confirms vacancy after Rod Culleton disqualified

Senate President confirms vacancy after Rod Culleton disqualified Mr Culleton has repeatedly denied he is bankrupt

Mr Culleton has repeatedly denied he is bankrupt One possible outcome is Mr Culleton's brother-in-law could take over his Senate position

The President of the Senate has written to the Western Australian Governor saying there is a vacancy in the Senate because Mr Culleton has been disqualified.

The Federal Court ruled last month that Mr Culleton was an "undischarged bankrupt".

Senate President Stephen Parry said in a statement he had received copies from the Federal Court Registry recording Mr Culleton as bankrupt.

He said Section 45 of the constitution provides an MP's seat becomes vacant if they are subject to a number of "disabilities", including bankruptcy, as set out in Section 44.

"It is a necessary and automatic consequence of the declaration of bankruptcy of a serving senator, that his place as a senator becomes vacant," Senator Parry wrote.

The Federal Court ordered a 21-day stay of proceedings following last month's court hearing which expires on Friday, but it is understood this does not affect the bankruptcy ruling itself.

However, Mr Culleton has repeatedly denied he is bankrupt, and has written a letter to Senator Parry objecting to the decision.

"The letter sent by you asserting that I am currently bankrupt and therefore disqualified to sit as a Senator ... is premature and should be withdrawn immediately," Mr Culleton wrote.

"I would also like to inform you that I am solvent and proof of that has been filed and evidence before the court.

"My application has already been filed, along with an appeal to extend the period of stay pending the hearing and determination of the appeal of the orders made against me.

"The letter should be withheld or if not withdrawn pending the outcome of the appeal."

Replacement hinges on Culleton's eligibility to run in first place

The High Court, sitting as the Court of Disputed Returns, may yet decide Mr Culleton was not eligible to even be a candidate, due to an outstanding conviction.

It is not known who his replacement might be, but it is possible his brother-in-law could take over his position.

Options for filling the vacancy include One Nation choosing a replacement candidate, or the position being allocated to the second person on the 2016 One Nation Senate ticket — Peter Georgiou, who is Mr Culleton's brother-in-law.

One Nation leader Pauline Hanson said she was ready to put up a replacement.

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There could also be a recount of votes.

Senator Parry said it would be necessary for the Court of Disputed Returns to decide whether Mr Culleton was ever eligible to become a senator in the first place, before it would become apparent how the vacancy might be filled.

It is believed the High Court will announce its ruling before Federal Parliament returns next month.

Mr Culleton parted ways with One Nation on December 18, citing "un-Australian behaviour" and "public rants" from the party.

He was embroiled in a public scuffle earlier this month as One Nation member Anthony Fels tried to serve him bankruptcy papers.

He fell to the ground and then sought hospital treatment for a wrist injury.

The ABC has attempted to contact Mr Culleton.