Former Nigerian military ruler Ibrahim Babangida is not seeking to be the ruling party’s presidential candidate in next year’s elections.
Mr Babangida was seen as one of the frontrunners for the April polls but his campaign is likely to be weaker without the ruling party’s support.
An aide said Mr Babangida had pulled out because President Olusegun Obasanjo said he would support a rival bid.
Political tension is high in Nigeria, with Mr Obasanjo standing down.
The announcement comes as the ruling People’s Democratic Party starts choosing from a shortlist of about 30 people to become its candidate.
Mr Babangida ruled for eight years until he was forced from power by popular protests in 1993 after he annulled elections that were described as the country’s freest and fairest yet.
The BBC’s Mannir Dan Ali in the capital, Abuja, says it is not clear whether Mr Babangida will become a candidate for another party, or back his close associate and former spy chief General Mohammed Aliyu Gusau for the PDP ticket.
Mr Babangida’s aide, retired Colonel Habibu Shuaibu, told the BBC that Mr Obasanjo’s backing for Katsina State Governor Umar Yaradua showed there was no level playing field in the PDP contest.
But PDP deputy national chairman Bode George insisted that the party did not have an anointed candidate.
Last week, Vice-President Atiku Abubakar withdrew from the PDP race.
He is expected to run on behalf of a rival party.