The Vatican said former pope Benedict XVI is overcoming a "painful but not grave ailment" that was "not particularly worrying".
It was responding to a German newspaper report that claimed the retired pontiff was seriously ill.
The clarification came hours after Benedict's biographer, Peter Seewald, sparked alarm by telling journalists that he had found the 93-year-old ex-pope "exceptionally frail" when he visited him on Saturday.
Mr Seewald said Benedict, who has been in poor health for sometime, was now suffering from shingles, a viral infection that causes painful rashes and is common among older people.
"The health conditions of the Pope Emeritus are not particularly worrying, apart from being those of an old man of 93 who is overcoming the most acute phase of a painful but not grave illness," said the statement from the Vatican.
Mr Seewald said Benedict's voice was barely audible - echoing something other visitors have said for months - and that the former pope told him he might pick up writing again if he regains his strength.
In June, Benedict, who lives in a former convent in the Vatican gardens, left Italy for the first time since his resignation in 2013 for an emotional farewell visit to his older brother Georg in their native Bavaria.
Georg Ratzinger died on 1 July aged 96. The two brothers were ordained priests on the same day in 1951.
Benedict, who was elected in 2005 to succeed the widely popular Pope John Paul II after a reign of nearly 27 years, shocked the world and even his closest aides when he announced he was stepping down on 11 February 2013,
He told a gathering of cardinals that he was too old and frail to lead an institution with more than 1.3 billion members.
At the time of Benedict's resignation, the Vatican was mired in a raft of financial woes, sexual abuse scandals and infighting among bureaucrats that led to leaks of important documents.
Benedict said his resignation was for exclusively health reasons.
He was succeeded by Argentinian-born Jorge Mario Bergoglio, now aged 83, who took the name Pope Francis.