Former Pope Benedict XVI became seriously ill following a visit to Germany in June, said German newspaper Passauer Neue Presse on Monday.
According to former pope's biographer Peter Seewald, the latter, 93, is suffering from erysipelas of the face, a virus that causes a facial itchiness and severe pain.
"According to Seewald, the Pope emeritus is now extremely frail," the report says.
"His thinking and his memory are quick, but his voice is hardly audible at the moment,” it added.
"At the meeting the emeritus Pope, despite his illness, was optimistic and declared that if his strength increased again he would possibly take up his pen again," the paper said.