Dr. David Uip, one of the doctors treating da Silva at Syrian-Lebanese Hospital in Sao Paulo, said he is suffering an infection that's predictable after radiation treatment, the Rio de Janeiro newspaper O Globo reported.
Da Silva, who served as president 2003-10, was being treated with intravenous antibiotics.
His last session of radiation treatment was Feb. 17.
Because of the treatment, he has suffered throat pain and hoarseness and has had difficulty swallowing.
Doctors have confirmed a tumor was removed from da Silva's throat and will perform tests, likely by the end of March, to determine whether there is cancer in his body.
Da Silva was diagnosed with cancer in October and has completed three rounds of chemotherapy and 33 sessions of radiotherapy.