Rome [Italy], June 20 (ANI): The cancellation of Pope Francis's trip to Africa has stirred speculation about his retirement.

The immobilized pope recently named a slew of new cardinals, raising questions about succession, reported The Wall Street Journal (WSJ).

Pope Francis' decided to call off a long-planned trip to Africa on account of a problem with his knee. Papal health has always been a concern at the Vatican, where the leader has traditionally ruled for life.

But since Pope Benedict XVI became the first pope in modern times to step down--a decision that Pope Francis has praised as an example to future pontiffs--it has become even harder to predict the end of a pontificate, reported WSJ.

More than nine years after his resignation, retired Pope Benedict, 95, is still living in the Vatican, increasingly frail yet by the accounts of visitors mentally acute.

While still active, Pope Francis, 85, has been seen frequently in a wheelchair for more than a month, telling the Italian daily Corriere della Sera in late May that he was suffering from a torn ligament in his knee, for which he was receiving injections.

He had to sit last Sunday through the Mass for Pentecost, a major church feast, delivering the homily from his wheelchair.

It wasn't until Friday that the Vatican issued a statement on the matter, announcing that his trip to the Democratic Republic of Congo and South Sudan, scheduled to begin in a little more than three weeks, had been indefinitely postponed.

The Vatican spokesman, Matteo Bruni, said the postponement came at the request of the pope's doctors, in order not to interfere with therapy on his knee, reported WSJ.

"It is highly unusual for any international trip to which the pope is committed to be cancelled, and certainly this close to the date," said John Allen, president of Crux Catholic Media, who said such a thing had not happened since the last years of St John Paul II, who died in 2005 after years of declining health.

St John Paul II increasingly delegated responsibilities to Vatican officials as he became incapacitated.

Coming almost a year after Pope Francis underwent surgery to remove part of his colon, and in the absence of any detailed information directly from physicians about that procedure or the knee ailment, rumors have flourished that the pope is hiding a serious illness. (ANI)