Malawi's former President Bakili Mukuzi is bidding to be named the candidate of the main opposition party in elections due next year.
His only challenger for the United Democratic Front ticket is Vice-President Cassim Chilumpha, who is under house arrest on treason charges.
Some 2,000 UDF delegates are due to choose between the two men.
But it is not clear whether Mr Muluzi would be eligible, as he served two terms before stepping down in 2004.
The constitution bans a president from serving more than two consecutive terms of office.
Mr Muluzi's supporters say this means he can now stand again but others disagree and the issue is likely to end up in court.
"In my own view, the spirit intended by the constitution was that a president can serve no more than two terms of office but it is a highly contested issue," constitutional expert Edge Kanyangolo told the BBC's Network Africa programme.
President Bingu wa Mutharika was elected as the UDF candidate in 2004 but soon afterwards fell out with Mr Muluzi, who remains party chairman.
Mr Mutharika then formed the Democratic Progressive Party (DPP).
Mr Muluzi told the BBC that Mr Mutharika had "forced" him to stand again, as he wanted the UDF to be in power.
"After 2004, my intention was to retire," he said, adding that if elected, he would only serve only term of office.
Mr Muluzi ended Hastings Banda's 30-year-rule in 1994, winning the country's first multi-party elections.
(BBC)
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