Dr. Juliet Cervantes told GMA News doctors are trying to treat an infection in Arroyo's intestines caused by her refusal to eat, a Gulf News report said Monday.
Arroyo, who was arrested Friday on charges of alleged electoral sabotage in 2007, has been hospitalized with hypoparathyroid bone disease.
She had attempted to leave the country for medical treatment last week before she was arrested.
On Tuesday, the country's Supreme Court will address a petition seeking to nullify the charges against Arroyo.
In another petition, filed Monday, Arroyo's husband, Mike, asked the high court to declare the charges and arrest illegal, ABS-CBN News reported.