Vatican spokesman Matteo Bruni on Friday released a report that Pope Francis will not honour his trip to Africa that was scheduled for July 2-7 to the Democratic Republic of Congo and South Sudan because of a knee ailment.

The decision to scrap his visit was taken "with regret" at the request of the pope's medical team who have been treating him for a torn ligament in his knee.

The pope has been using a wheelchair for the last one month, although he has been on his toes to cover his official duties including a meeting on Friday with European Commission President Ursula von der Leyen.

Vatican sources have said the pope has been receiving several injections a week for the ailment, as well as physical therapy, and that he had hoped to be able to regain at least partial ability to walk before the trip was due to start.

The surprise announcement came just two days after the Vatican released the names of journalists whose requests to accompany the pope on the papal plane had been accepted and preparations in both countries were well underway.

The trip to the Democratic Republic of Congo and South Sudan in the summer heat would have been difficult for the 85-year-old pontiff under normal circumstances but mobility problems would have made it excessively stressful.

It would have entailed five plane journeys and three Masses that would have required him to remain standing for long periods. He was also due to make more than a dozen addresses, meet political officials and Church groups and visit camps for displaced people in both countries.

His condition improved for a while but several times in the past few weeks, he was forced to delegate the celebration of papal Masses to a senior cardinal while he remained seated and read the homily.