Doctors had drained an accumulation of liquid in the area where the colostomy bag had been previously removed during the surgery, his spokesman said, cited by the BBC.
Bolsonaro has no pain or fever, however, he will not leave the hospital before Monday of next week, the spokesman added.
Bolsonaro, who took office as the new president of Brazil on 1 January, has been given antibiotics and continues to perform breathing and muscle-strengthening exercises in his bedroom, his doctors said in a medical report.
The president, 63, checked into São Paulo's Hospital Israelita Albert Einstein on 27 January in preparation for surgery and is expected to make a full recovery, and to leave the hospital after 10 days.
Earlier on Monday, Mr Bolsonaro posted a video of himself on Twitter doing physiotherapy exercises in bed.