Jair Bolsonaro has been hospitalised with pneumonia a week after an operation to remove a colostomy bag.
The country's leader was struck down with a fever during his hospital stay, but a tweet on his account yesterday
said he was 'well'.
Bolsonaro, 63, had an operation on January 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 hospital for 10 days, but this week his spokesman said he would remain hospitalized at least until February 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 38C (100.4F) 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.