Pope Francis cancelled a visit to a Rome hospital today where he was scheduled to observe Mass.
The Vatican issued a two-sentence statement in Italian saying the pontiff would be unable to visit Gemelli Hospital in Rome this afternoon "due to a sudden indisposition."
Pope Francis, 77, had been scheduled to visit the hospital from 1:30 p.m. until 4 p.m. GMT today. He was also expected to visit the Medicine Faculty at the Catholic University of the Sacred Heart, which is located at the hospital.
Cardinal Angelo Scola, archbishop of Milan, will visit the hospital in the pontiff's place, according to the Vatican. It is expected Scola will observe Mass and read the Pope's homily.
The Argentinean-born pope had part of one lung removed when he was a teenager because of an infection.
Earlier this month, he missed two days of audiences due to what the Vatican said was a stomach bug. Last week, Pope Francis skipped walking in a mile-long procession and decided to rest up for a trip to Italy.
The Associated Press contributed to this report.