Pope Francis has cancelled his participation in a yearly Mass and procession next weekend due to ongoing knee pain, the Vatican said.

The annual Corpus Domini procession, scheduled for Sunday, is a centuries-old profession of the Catholic faith during which the Eucharist is exhibited publicly.

Francis has cancelled several events this year due to the strained ligaments in his right knee that have made walking and standing difficult.

He has been using a wheelchair for over a month and the Vatican last week announced he had to cancel his planned July 2-7 trip to Africa in order not to jeopardise his recovery.

On Sunday, Francis apologised to the governments and faithful in Congo and South Sudan, saying he was upset that he had to postpone the visit and that the trip really meant a lot to him.

“I apologise to you,” he said, asking for prayers “so that with the help of God and medical treatment I can come to you as soon as possible”.

The Vatican has not specified the exact nature of the problem or what treatments Francis is receiving, but he has said he has received some injections and friends say he is doing physical therapy daily.