Nigeria's electoral commission is to publish the official list of candidates for next month"s presidential election.
But Vice-President Atiku Abubakar, who is facing corruption charges, is set not to be included.
Electoral officials say the charges mean Mr Abubakar is constitutionally barred from standing for election.
Mr Abubakar, standing as an opposition candidate after falling out with former ally President Obasanjo, has said he will challenge the decision in court.
Despite a high court ruling that the commission cannot disqualify candidates, electoral officials say Mr Abubakar is barred by the constitution, unless he manages to get a court to dismiss government accusations of corruption against him.
So the whole issue of whether he can stand will be resolved in the courts, but there is one rather large problem: time is running out.
There are just five weeks to go before the election; ballot papers will have to be printed and delivered soon, given that there are some 60 million registered voters spread throughout the country.
There is the real risk that these elections will be mired in messy court cases and legal challenges, both before and after the votes are cast.
The vice-president's party, the Action Congress, says the position of the Independent National Electoral Commission is leading Nigeria towards anarchy.
The Action Congress is one of the two main opposition parties contesting the election, and continues to hold mass rallies around the country, despite the threat to its candidates' presidential ambitions.