Brazil has the world's second-largest outbreak behind the United States. Latin America's largest country has more than 1.6 million confirmed cases and 65 000 Covid-19 deaths.
Bolsonaro has repeatedly defied local guidelines to wear a mask in public, even after a judge ordered him to do so in late June. Bolsonaro has also railed against social distancing rules supported by the World Health Organisation.
Over the weekend, Bolsonaro attended several events and was in close contact with US Ambassador Todd Chapman during 4 July celebrations. Pictures showed neither wearing a mask.
The U.S. embassy in Brasilia said via Twitter on Monday that the ambassador had lunch on 4 July with Bolsonaro, five ministers and the president's son, Congressman Eduardo Bolsonaro. The ambassador had no symptoms, but would undergo testing and is "taking precautions," the embassy said.