Pope Francis cleared his schedule on April 22 to undergo medical tests.

The Pope has been forced to curtail his activities recently because of health problems. He was not the principal celebrant at the Easter Vigil in St. Peter’s basilica, and sat down midway through his Urbi et Orbi address on Easter Sunday.

A painful knee—which Vatican officials have attributed to strained ligaments—has made it difficult for the Pontiff to move or stand, and he has been assisted in walking for weeks. Last July he was hospitalized for an operation in which surgeons removed about a foot of his colon. The Vatican has not disclosed any other medical problems.

Although he has admitted that his health is “capricious,” and his schedule is therefore uncertain, the 85-year-old Pontiff has planned trips later this year to Lebanon and to Africa, and he has voiced his desire to travel to Canada.