ROME -- Pope Francis cancelled his participation in a religious procession due to ongoing knee pain. However, he said Monday that he hopes to celebrate a special Mass to the Congolese community in Italy after having to postpone his planned trip to Africa.

"We'll take Kinshasa over to St. Peter's," Francis said to a group missionary priests, The White Fathers, Monday during an audience.

He admitted that he was disappointed to have to cancel his July 2-7 trip to Congo and South Sudan, but said he still hoped to make it to Rome's large Congolese community for a Mass at The Vatican on July 3.

He said, "At my age, it's not so simple to go on mission," to the priests who have been ministering in Africa for many years.

Francis has cancelled his participation in many events this year because of the strained ligaments that have affected his right knee. This makes it difficult for him to walk and stand. Francis has been in a wheelchair for more than a month. The Vatican announced last week that he had to cancel his trip to South Sudan and Congo because of his injuries.

The Vatican announced Monday that Francis would have to also bow out of Sunday's Corpus Domini procession. This is an annual, centuries-old, professing of Catholic faith, during which the Eucharist will be displayed publicly.

Francis apologized to South Sudanese and Congo government faithful and asked for prayers on Sunday "so that with God's help and medical treatment, I can get to you as soon and as possible."

Francis has not yet been given any details by the Vatican about the nature of his problem or the treatments he is receiving. However, he said that he had received injections and that he is getting physical therapy every day.