Pope Benedict XVI of the Roman Catholic Church resigned in 2013 due to advancing age.
Pope Francis has asked for prayers for his predecessor, Benedict XVI, saying he is “very sick”.
Francis made the surprise appeal on Wednesday at the end of his general audience, giving no details.
Benedict, 95, resigned from his post due to advancing age in 2013 and became the first pope in about 600 years to do so. He has been living in the Vatican since then.
“I would like to ask all of you for a special prayer for Pope Emeritus Benedict, who, in silence, is sustaining the church,” Francis said, speaking in Italian.
“Let us remember him. He is very sick, asking the Lord to console and sustain him in this witness of love for the church, until the end,” he added.
Vatican spokesperson Matteo Bruni said Pope Francis went to visit his predecessor.
“Regarding the health conditions of the emeritus pope, for whom Pope Francis asked for prayers at the end of his general audience this morning, I can confirm that in the last hours, a worsening due to advanced age has happened,” Bruni said in a written statement.
“The situation at the moment remains under control, constantly monitored by doctors,” according to the statement.
Exceptionally weak
Until a few weeks ago, those who had seen Benedict said his body was very frail but his mind was still sharp.
One of the latest known photographs of Benedict was taken on December 1, when he met the winners of a prize for theologians named after him. He was seated and looked exceptionally weak.
Since his resignation Benedict has been living in a former convent inside the Vatican gardens, with his secretary, Archbishop Georg Ganswein, and a few other aides and medical staff.
Benedict announced his intention to resign on February 11, 2013, shocking a meeting of cardinals. He said he no longer had the physical and mental strength to run the church.
He formally stepped down on February 28 that year, moving temporarily to the papal summer residence south of Rome while cardinals from around the world came to Rome to choose his successor.
‘Safe pair of hands’
Francis, the first pope from Latin America, was elected to succeed him on March 13, 2013.
While Francis has often praised the former pope, saying it was like having a grandfather in a home, the presence of two men dressed in white in the Vatican was at times troublesome.
Conservatives looked to the former pope as their standard bearer and some ultra-traditionalists even refused to acknowledge Francis as a legitimate pontiff.
Benedict, the first German pope in 1,000 years, was elected on April 19, 2005 to succeed the widely popular Pope John Paul II, who reigned for 27 years.
Cardinals chose him from among their number seeking continuity and what one called “a safe pair of hands”.
For nearly 25 years, as Cardinal Joseph Ratzinger, he was the powerful head of the Vatican’s doctrinal office, then known as the Congregation for the Doctrine of the Faith (CDF).