France's answer to Elvis Presley checked into a private hospital in western Paris early Monday morning.
A musical icon known simply as "Johnny" at home, Hallyday has sold more than 100 million records in his decades-long career.
The 74-year-old announced in March that he was being treated for cancer but said his life was not in danger.
During his stay in hospital Hallyday received numerous visits from his family including his daughter Laura Smet and manager Sebastian Farran, who said on Friday his condition had "stabilised".
The star's early concerts in the 1960s prompted scenes of hysteria similar to those seen at shows by the Beatles and the Rolling Stones as the rock 'n' roll revolution swept the Western world.
Hallyday is also known for an eventful private life and a row over his decision to dodge French taxes by taking up residence in Switzerland.
His major hits, almost always sung in French, include local versions of Presley's "Hound Dog", "Let's Twist Again" by Chubby Checker and "Bebop a Lula" by Gene Vincent.