The 93-year-old retired pontiff is said to have had a facial infection since returning to Rome after a visit to Germany.
Former Pope Benedict XVI is ill with shingles after returning to the Vatican from a visit to Germany, a newspaper citing his biographer has reported.
The 93-year-old retired pontiff has become very frail and his voice is barely audible, author Peter Seewald told German daily Passauer Neue Presse.
However, German-born Benedict met with Mr Seewald on Saturday and appeared optimistic, adding that he might pick up writing again if he regains his strength, according to the paper.
Benedict visited his native Bavaria in June to pay his ailing brother Reverend Georg Ratzinger a final visit.
Mr Ratzinger, aged 96, died shortly afterwards.
It was Benedict’s first trip outside Italy since 2013, the year he resigned the papacy.
The retired pope has lived in a monastery in Vatican City since shortly after his retirement.
Elected to the papacy in 2005 to succeed St John Paul II, the former Joseph Ratzinger was the first pontiff in 600 years to resign the post.
He was succeeded by Pope Francis.