A militant group in Zimbabwe's ruling party has threatened former Finance Minister Simba Makoni, who is running for president as an independent.
Simba Makoni could appeal to Zanu-PF and opposition supporters
"Traitors should know Zanu-PF [ruling party] has a history of dealing harshly with their kind," Joseph Chinotimba of the war veterans' association said.
The group was at the forefront of the sometimes violent campaign of invading white-owned land, starting in 2000.
Mr Makoni said he would stand against President Robert Mugabe in March.
Senior Zanu-PF officials have said that Mr Makoni had expelled himself from the party by saying he would stand as an independent.
He was a member of its decision-making body, the politburo.
Mr Makoni, 57, said he would have liked to contest the election on behalf of Zanu-PF but also blamed its leaders for Zimbabwe's economic crisis.
"I share the agony and anguish of all citizens over the extreme hardships that we all have endured for nearly 10 years now," he said.
1980: Named deputy minister aged 30
2002: Sacked as finance minister after argument with Mugabe
2002: Went to South Africa
Possible support of Zanu-PF heavyweight Solomon Mujuru
"I also share the widely held view that these hardships are a result of failure of national leadership and that change at that level is a pre-requisite for change at other levels of national endeavour."
He has long been seen as a possible compromise candidate, who could appeal to moderate Zanu-PF supporters, as well as opposition sympathisers.
The two opposition Movement for Democratic Change (MDC) factions are each fielding candidates in the election.
The BBC's Peter Greste says Mr Makoni could pose a stronger challenge to President Mugabe than the divided opposition.
But our correspondent notes the former finance minister is standing as an independent and so will not have access to any of the resources of the ruling party or the state to help his campaign.
He is believed to have the backing of Zanu-PF heavyweight Solomon Mujuru, whose wife Joyce is vice-president.
After 18 months as finance minister, he was sacked in 2002 over policy differences with Mr Mugabe.
The MDC had insisted on a new constitution before the elections, as well as guarantees they would be free and fair.
Previous polls have been characterised by violence and allegations of fraud.
Zimbabwe has the world's highest annual rate of inflation - 26,000% - and only an estimated one adult in five has a job.
Mr Mugabe's critics blame the economic crisis on his policies, especially the seizure of white-owned farms.
He blames a western plot to bring him down.