The replacement for Bob Day in the Senate might not be known for several weeks, with no guarantee it will be a Family First member either.
The High Court will also look into whether Mr Day breached the constitution when he was elected on July 2.
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There are concerns he had a financial interest in the building of his Adelaide electorate office, which was taxpayer funded.
If proven there was a vested interest, that could disqualify him from being eligible to stand as a member of the parliament, in accordance with section 44 of the constitution.
The Attorney-General, George Brandis, is expected to ask the Senate to refer the matter to the High Court on Monday.
If it accepts the case, the court will decide if Mr Day was duly elected, or if not, force a recount of the South Australian Senate vote.
In previous instances, the number two candidate has been handed the seat, but the court will have to rule whether the Family First ticket was still valid with just one person.
If the entire ticket was excluded in the recount, the last spot would be battled out for by Labor and One Nation.
Mr Day’s support has been relied on by the federal government for a number of key pieces of legislation.