The Pope has briefly greeted visitors while being taken on an unannounced visit to St Peter's Basilica.
He was seen without his usual papal attire and with a blanket draped around his shoulders.
The 88 year old also had an oxygen tube attached to his nose.
Bystander Luiz Gill said:
"We were visiting St. Peter's Basilica and saw some guards passing by and making way, so we went to see what it was, and it was the Pope. Few people noticed, it was very quick, but he stopped to talk to a family with a baby."
It's been a busy week for the pontiff, who met the King and Queen at the Vatican on Wednesday. He's under medical orders to rest for two months after spending five weeks in Rome's Gemelli hospital where he was treated for a life-threatening bout of double pneumonia.