Zimbabwe's former Finance Minister Simba Makoni has said he does not want to form an alliance against President Robert Mugabe in next month's polls.
Simba Makoni was a senior Zanu-PF official until this month
He did not want to alienate potential supporters within the ruling Zanu-PF party, he told South African radio.
Analysts says that a coalition would stand a stronger chance of defeating Mr Mugabe, who has been in power since independence in 1980.
Opposition leader Morgan Tsvangirai has also ruled out an alliance.
But a faction of Mr Tsvangirai's party is backing Mr Makoni in the 29 March presidential election.
"There are a large number of people in Zanu-PF who share my proper vision," Mr Makoni told South Africa's Talk Radio 702.
"I don't want to alienate those people by forming a coalition with one entity."
He was in the party's decision-making body until he was expelled for saying he would stand against Mr Mugabe as an independent.
Both Mr Mugabe and Mr Tsvangirai launched their campaigns at the weekend.
Mr Mugabe's launch coincided with the celebration of his 84th birthday.
Mugabe has ruled Zimbabwe since independence in 1980
Zimbabwe is suffering an economic crisis, with annual inflation of 100,000% and unemployment at 80%. There are also severe food and fuel shortages.
Many of Zimbabwe's problems have been blamed by the opposition and Western countries on the policies of President Mugabe.
But he told his supporters that his party would win the elections "resoundingly" and he was ready for a fight with those who criticised his presidency, including US President George W Bush and British Prime Minister Gordon Brown.
"It is the sanctions that they have imposed which have caused a great deal of harm on the economy," he said.
The EU and US have imposed a travel ban and seized assets belonging to Mr Mugabe and his close associates but have not imposed economic sanctions on Zimbabwe.
Launching his campaign before thousands of supporters in Mutare, Mr Tsvangirai said: "All of Zimbabwe is in the custody of a dictatorship. We're all bleeding, but we're marching on. We're weak and with hunger, but we're stronger with anger."
He said the Zimbabwean economy was "an enclave economy that is uneven, unequal and virtually dead".
"Zimbabwe is one of the world's great humanitarian crises," he said.