Pope Francis cancelled his appointments on Friday to undergo medical examinations, Vatican spokesperson Matteo Bruni said.
The Vatican did not say what ailment caused the pope to clear his calendar, although the 85-year-old had been struggling with problems in his right knee for some time.
Climbing stairs and walking longer distances had become strenuous for him.
Francis has a noticeable limp.
During the recent Easter celebrations, he often sat and could not stand for long.
