The former pope Benedict is “very sick,” according to the Vatican.
His successor Pope Francis asked people to pray for him at his general audience this morning.
“I'd like to ask all of you for a special prayer for Emeritus Pope Benedict, who, in silence, is sustaining the church,” Pope Francis said in his remarks.
“I remind you that he is very sick.
“Let's ask the Lord to comfort him and sustain him in this testimony of love to the church to the very end.”
He did not elaborate on his predecessor’s condition; however, the Vatican has confirmed that he has had a sudden "worsening" of his health in recent hours.
Pope Francis went to visit Benedict after the service.
The 95-year-year-old pope emeritus became the first pope in some 600 years to resign back in 2013.
He has been living in the Vatican since then.
A Vatican spokesperson said he is receiving constant medical care and his condition is "under control".
With reporting from IRN.