He had originally been expected to stay in the hospital for 10 days but his spokesman said he would remain hospitalized at least until Feb. 11 because of a fever and other complications.
Far-right Brazilian President Jair Bolsonaro has pneumonia after registering a fever during a hospital stay, but a tweet on the far-right leader's Twitter profile on Thursday said he was "well."
Bolsonaro had an operation on Jan. 28 to remove a colostomy bag that was put in place after he was stabbed while campaigning ahead of Brazil's election last year.
He had originally been expected to stay in the hospital for 10 days but this week his spokesman said he would remain hospitalized at least until Feb. 11 because of a fever and other complications.
A tweet on Bolsonaro's Twitter profile said: "Be careful not to be sensationalist. We are very relaxed, well and remain steady."
The Albert Einstein hospital in Sao Paulo said in a statement on Thursday that doctors had adjusted his antibiotics dose after a fever late on Wednesday.
Presidential spokesman Otavio Rego Barros said at a news conference that the president was in semi-intensive care. He said Bolsonaro had a 38 degree Celsius (100.4°F) fever on Wednesday and bacterial pneumonia.
If the president is unable to carry out his duties, then Vice President Hamilton Mourao, a retired general who has already clashed with Bolsonaro over a number of issues, would take charge.