Zimbabwe's ruling party has expelled ex-Finance Minister Simba Makoni who announced he would challenge Robert Mugabe for the presidency in March.
An opposition faction has ruled out an alliance with Mr Makoni
"The rules are very clear that anyone who tries to challenge an elected candidate of the party stands expelled," a Zanu-PF spokesman said.
President Mugabe will face three challengers as both factions of the opposition are fielding candidates.
The 83-year-old president told state TV was "raring to go" in the polls.
"I am very raring to go and raring to fly," the state-owned Herald newspaper quotes him as saying.
He predicted he would win a landslide victory on 29 March.
Mr Makoni's status within Zanu-PF has been unclear since a ruling party official said he had effectively expelled himself after announcing last week that he would stand as an independent.
"It was decided to make the expulsion of Simba Makoni clear," Nathan Shamuyarira, a Zanu-PF spokesman, said at a news conference.
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
"In the case of Simba Makoni... he stands expelled," he said.
After 18 months as finance minister, Mr Makoni was sacked in 2002 over policy differences with Mr Mugabe.
Mr Shamuyarira added that anyone in Zanu-PF who decided to back Mr Makoni would also be expelled.
He is thought to have the backing of the former army chief Solomon Mujuru, whose wife Joyce is vice-president.
The 57-year-old is expected to launch his election manifesto this week and has said he will not be fighting the election alone.
On Monday, Zimbabwe's main opposition leader Morgan Tsvangirai said he would not join forces with Mr Makoni, who he described as "old wine in a new bottle".
There had been speculation that Mr Tsvangirai could stand aside to let Mr Makoni be the main anti-Mugabe challenger.
There are also reports that Arthur Mutambara, from the other faction of the Movement for Democratic Change, could join forces with Mr Makoni.
The MDC had been insisting 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.