Dubbed 'France's Frank Sinatra', Aznavour is one of the country's best-known and beloved singers, whose ballads are recognized the world over.
"Charles Aznavour has been preventively hospitalized after contracting an infection in recent days," the Opus One event managers said in a statement, without providing more details about his condition or which country or hospital he was being treated in.
The activist-singer's planned concert in Geneva on Friday evening was postponed, but he and the organizers would try to reschedule the concert "as soon as possible," the statement said.
Aznavour lives in Switzerland, having built a lakeside house near Lausanne in the canton of Vaud to be closer to his youngest son Nicolas, a scientist at the Swiss Federal Institute of Technology at Lausanne (EPFL).
Aznavour, who began performing at the age of nine, has penned nearly 1,000 songs over his career.
"Everything interests me, really everything . . . I read every day," he told Swiss public broadcaster RTS at the weekend.
"I have three books: a book I have to read, a book where I learn something and I have foreign language texts that I work on regularly," Aznavour said.
"Over the past two months we have travelled to ten capitals," he said, insisting though that it was not a farewell tour.
"I'll be back next time."