Bolsonaro, an ex-army officer who has repeatedly expressed support for Brazil's former dictatorship, is poised in the polls to win a second round of voting later this month.
But a senior administration official, speaking on condition of anonymity, said that "Brazil has very strong democratic institutions."
"We're not particularly concerned in that sense," he told reporters. "We feel confident in the will of its (Brazil's) people."
Bolsonaro is leading leftist Fernando Haddad in the October 28 runoff, following a crushing first round victory.
He rejects the "far-right" label and says he is an "admirer" of US President Donald Trump.
However, Bolsonaro has a long history of comments demeaning women and gays, and speaking in favor of torture and Brazil's 1964-1985 military dictatorship. He belongs to the ultra-conservative Social Liberal Party.
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