Addressing a press conference at his blue roof mansion in the plush Harare suburb of Borrowdale, Mugabe said people should respect the outcome of tomorrow's election.
"I was sacked from the party that I founded...with the likes of [former vice president Simon] Muzenda and others".
In a media briefing on Sunday, Chamisa said the elections were just a formality as he prepares for the inauguration after the elections.
Referring to current president Emmerson Mnangagwa, who took office with the military's support, the 94-year-old told reporters on Sunday: "I can not vote for those who have tormented me".
Zimbabwe's military generals shocked the world in November when they seized control and ushered Mnangagwa to power after Mugabe, who is in frail health, tried to position his wife Grace, 53, to be his successor. "Those tanks that rolled through across the country, who were they fighting?"
Mugabe, one of the last "Big Men" of African politics, still looms large over Zimbabwean politics and he may yet influence the first vote without his name on the ballot paper since the country gained independence from Britain in 1980.
He said he wished whoever wins well. Experts say the current election campaign has been the most peaceful for many decades.
He indicated, however, that Chamisa was the only viable candidate.
Mnangagwa, who is accused of involvement in election violence and fraud under Mugabe, has vowed to hold a fair vote and invited in worldwide observers - including the previously-banned European Union team.
He swore he would not support the ruling party he controlled for decades at the polls, saying: "I can not vote for ZANU-PF".
"Today we unlock the potential of our beloved homeland to build a new Zimbabwe for all", he said, repeating his promise of economic revival.
With 5.6 million registered voters, the results of the presidential, parliamentary and local elections are due by August 4.
If no candidate wins more than 50 percent of the vote, a runoff will be held on September 8.