"I would like to ask all of you for a special prayer for Pope Emeritus Benedict, who, in silence, is sustaining the Church. Let us remember him," Pope Francis said.
"He is very sick, asking the Lord to console and sustain him in this witness of love for the Church, until the end."
In 2013, Benedict became the first pope in some 600 years to resign.
Who is former pope Benedict?
Born as Joseph Ratzinger in the southeastern German state of Bavaria, he became leader of the Catholic Church in 2005.
Benedict, 95, lives in the Vatican.
The former pope has been at the center of sex abuse scandals involving the Catholic Church. Early this year, he admitted to giving false testimony in an investigation in the Munich archdiocese, which he said was unintentional.
