Pope John Paul II’s doctors were on guard for complications Wednesday, a day after the 84-year-old pontiff was hospitalized with the flu and breathing trouble.

Pneumonia remained a potentially lethal threat, but the Vatican said there was “no cause for alarm.”

The pope will remain hospitalized for a few more days as a precaution, the Vatican said.

A spokesman said the pope’s inability to hold his back straight, a consequence of his Parkinson’s disease and other ailments, has compressed his lungs and diaphragm.

Tests showed the pope’s heart and breathing to be normal.