In late December, Bolsonaro went to the US to spend New Year's Eve at former US President Donald Trump's Mar-a-Lago resort in Florida.
Bolsonaro neither participated in the inauguration of his successor Luiz Inacio Lula da Silva on January 1 nor intended to hand over the presidential sash.
Ned Price, spokesperson for the US State Department, noted on Monday that the agency was aware of the reports but that the department would not comment on them.
"I am aware of the reports that he has been hospitalized," Price told a briefing. "Of course, he is a private citizen, so we wouldn’t comment on that from here."
Bolsonaro has had health problems since an assassination attempt in 2018, when he was stabbed during a campaign rally in the town of Juiz de Fora, about 125 miles north of Rio de Janeiro, nearly a month before the election. The knife damaged the mesenteric artery, which provides blood supply to the intestines. He underwent several surgeries afterward.