Carlos Marun is close ally of the president. He said today he did not think the issue was serious but did not provide any more details.
Earlier this month, Temer's office announced that he had been diagnosed with a partial coronary obstruction that would be treated with aspirin and a low-fat diet.
Local media is reporting that the 77-year-old president's new hospitalisation isn't related to his heart condition.
Temer is facing a vote in the lower house of Congress today that could see him suspended and put on trial on corruption charges.