Pope Leo was due to be hospitalised in Rome on Tuesday ahead of surgery to remove a small growth on one of his lungs, in the first major health issue of his 17-month tenure.
Leo, 71, said on Sunday that a small nodule had been found on a check-up, was "well-contained" and had been spotted early.
He was expected to leave the Vatican for Rome's Gemelli hospital late morning, the Vatican press office said, without specifying when the actual operation would take place.
Leo, elected by the world's cardinals in May 2025, is relatively young for a Church leader. He enjoys sports, including tennis, and is not known to be a smoker or to have had health issues previously.
The Vatican has said his recovery is expected to take about a week. All his public events have been cancelled until Oct 20.
A nodule on the lung is a small, localised lesion that can be benign. The American Thoracic Society says fewer than 5 percent of lung nodules overall prove cancerous, although risk rises with age, size, and other factors such as smoking.
Dr Federico Venuto, chief of thoracic surgery at Rome's Policlinico Umberto I hospital, said procedures to remove lung nodules are usually minimally invasive, and can sometimes involve use of a thin camera tube called a thoracoscope.
"The complication rate is extremely low," he told Reuters.
The late Pope Francis, Leo's predecessor, died at age 88 in April 2025 and was hospitalised several times as he grew frail in his later years.
Leo, who spoke in a firm, clear voice at his only public event on Monday, keeps a very busy schedule. He is due to make an 11-day tour of Uruguay, Argentina and Peru from Nov 6 to 17.
In the same address on Sunday when the pope announced his need for surgery, Leo pledged he would go forward with the trip.