Veteran French crooner Johnny Hallyday admits to having cancer but denies it is life-threatening

Veteran French rocker Johnny Hallyday has announced that he is being treated for cancer, just hours before a glossy magazine was due to reveal his illness, describing it as a serious concern.

"Johnny" - as his fans call the closest France has got to Elvis who is often dubbed "the biggest star you've never heard of" - was quick to reassure followers on Twitter that his life was not in danger.

"I was actually screened a few months ago for cancer cells for which I am currently being treated," he wrote.    

"My life is not in danger today," added the 73-year-old.    

"I'm doing very well and am in good physical condition," he added.     

Hallyday's announcement came ahead of the publication on Thursday by Closer magazine, which claimed his condition was life threatening.    

British rock lovers may scoff, but Johnny enjoys cult following back home, having sold more than 100 million records in his decades-long career.   

His health has been the subject of media speculation since he was hospitalised in 2009 in the United States for complications following a hernia operation, and was put in an artificial coma.    

Hallyday is a colourful character loved for hits such as "Allumez le Feu", but also home-grown versions of rock standards such as Elvis Presley's Hound Dog and Bebop a Lula by Gene Vincent.

But he has also sparked considerable controversy, in particular for choosing to dodge French taxes by taking up residence in Switzerland, saying he had had enough of being "fleeced" back home.     

Part of the "Ye Ye" generation, Hallyday's career took off in 1960, where he prompted the same scenes of hysteria in France as the Beatles or the Rolling Stones.   

Fans wished the veteran rocker well on social media.    

"Good luck with this fight," one wrote on Twitter. "While music lives, you'll always be there Johnny. Get well soon, we love you," wrote another.