Bolsonaro has infamously likened the virus to a "little flu", amid attacks on stay-at-home measures and other public health guidelines.
Brazilian President Jair Bolsonaro has again tested positive for the new coronavirus, his office announced, saying he would extend his two-week quarantine and suspend upcoming travel plans.
The far-right leader, who has faced criticism for downplaying the pandemic and flouting social distancing measures, has been in self-isolation in the presidential palace in Brasilia since first testing positive for the virus on July 7.
"President Jair Bolsonaro's health continues to improve, under the treatment of the presidential medical team," his office said in a statement.
"A (new coronavirus) test carried out yesterday on the president came back positive."
Bolsonaro, 65, has famously compared the virus to a "little flu" and attacked stay-at-home measures and other guidelines from public-health officials.
Until he was infected, he regularly hit the streets of Brasilia without a face mask, exchanging hugs and handshakes with supporters and urging Latin America's biggest country to get back to work despite its rapidly spreading outbreak.
Since testing positive after developing a fever and fatigue, he has been working by video conference from the presidential residence, the Alvorada Palace -- a routine he admitted last week he "can't stand."
Following the latest positive test result, his third since getting infected, Bolsonaro "indefinitely postponed" upcoming trips to the north-eastern states of Piaui and Bahia, his office told AFP.
On Sunday, Bolsonaro greeted supporters at his residence, separated by a reflecting pool about two meters (six-and-a-half feet) wide.
He removed his face mask to talk to them and proudly held up a box of hydroxychloroquine, the anti-malaria drug he is taking against the infection.
Both Bolsonaro and US President Donald Trump, whom he admires, have touted the medication as a treatment for COVID-19, despite scientific evidence it is ineffective against coronavirus.
Bolsonaro's hydroxychloroquine box-brandishing incident was "deplorable," said respiratory specialist Margareth Dalcomo, of Brazil's leading public-health institute, Fiocruz.
"This politicization of the drug by the US and Brazilian presidents for murky reasons has no justification, and it deceives people," she told AFP.
"It has been proven this drug has no effect against COVID-19.... And it has potentially serious side-effects."
Brazil is the country hit second-hardest by the pandemic, after the United States. It has recorded nearly 2.2 million infections and more than 80,000 deaths.