"Experience has shown... there will be a second round" after the October 25 vote, meant to end a four-year political crisis, he said in an interview with foreign media, including AFP.
He ruled out a return of his rival, ex-president Marc Ravalomanana whom he overthrew in 2009, but he did not dismiss a possible future turn as prime minister for himself.
"It is not yet on the agenda, we will try to see the election outcome, how the situation evolves," he said before adding: "I do not exclude it either."
After the October presidential poll, a parliamentary vote will follow on December 20, along with a second presidential round if there is no outright winner.
The former mayor of Antananarivo declined to say which of the 33 candidates he supported.
He assured he had "no regrets" after having been forced under international pressure to pull out of the polls, along with former head of state Didier Ratsiraka and former first lady Lalao Ravalomanana.
Exiled in South Africa since the coup in 2009, Ravalomanana has tried several times to return to the island.
Rajoelina said it would be wise to "let the people choose and then we'll see how things will develop."
An electoral court last month disqualified the three controversial candidates from the election race after the trio refused to withdraw.
Their candidacies, which did not meet electoral rules, had been widely condemned.