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.