Rainier's health "remained worrying," three of his doctors said in a statement. "Because of the fragility of his cardiac, respiratory and kidney functions, the vital prognosis remains reserved."
The statement indicated that specialists were withholding a prognosis, meaning they are unsure he will recover.
Dr. Jean-Charles Piette, chief of internal medicine at La Pitie Salpetriere hospital in Paris, was asked to examine Rainier, the statement said. He and other specialists decided the prince must continue his current course of treatment.
Piette examined Rainier on Thursday night, said palace spokesman Armand Deus.
Rainier was hospitalized more than two weeks ago with a chest infection. His health suddenly worsened on Tuesday, and he was brought to the intensive care unit of Monaco's seaside Cardio-Thoracic Center.
Boyan Christophorov, a professor of internal medicine at Paris V University, said the phrasing of Rainier's medical bulletin suggested that his doctors seriously fear for the prince's life. "The terms of these releases are carefully weighed. That the patient's vital prognostic is 'reserved' means that his life is seriously threatened," Christophorov told the Associated Press.
At a service Thursday evening at Monaco's Sainte Devote church, the Rev. Fabrice Gallo asked worshippers to pray for Rainier, and priests at Good Friday services in Monaco requested more prayers for Rainier, Deus said.