French rocker Johnny Hallyday, who has been hospitalized in Los Angeles, has taken legal action to determine whether his Paris surgeon was at fault over a previous operation for back trouble, his publicists said on Thursday.

One of France's most popular entertainers in a career spanning almost 50 years, Hallyday, 66, was admitted to the Cedars-Sinai hospital last week, complaining of severe pain shortly after arriving from Paris.

He was subsequently operated on to repair lesions opened up from the earlier procedure in November for a herniated disc -- commonly known as a slipped disc -- and was put into an artificial coma to relieve his pain.

French news bulletins have been dominated for days by unclear and contradictory reports about the condition of the singer, who has suffered from a succession of health problems in recent months.

A statement from his publicists said Hallyday and his wife Laeticia had decided to start civil proceedings against Dr Stephane Delajoux, who performed the operation on November 29, and the Clinique Internationale du Parc Monceau.

This procedure aims to have the justice system engage independent experts to conduct an investigation under cross-examination of the circumstances of the November 29 operation and to examine whether they conformed with the rules of medical science, it said.

It said an initial hearing would be held on December 21.

The Clinique Internationale du Parc Monceau, a private clinic in an exclusive part of Paris, declined to comment but a lawyer for Delajoux welcomed the move and said his client was confident an investigation would show he had not been at fault.

As Dr Delajoux is extremely calm regarding the operation he performed on Mr Hallyday, it will be seen that it was not due to any fault on the part of the practitioner that Mr Hallyday is in the condition he is in, which is obviously regrettable, David Koubbi told Reuters.

Numerous French celebrities including veteran crooner Charles Aznavour have flown to Hallyday's bedside and the case has even drawn comment from President Nicolas Sarkozy, who spoke at some length about the singer at a recent press conference.

Hallyday, who began his career in the 1960s as one of France's first teenage rock stars, is particularly famous for his energetic live performances and he has been forced to cancel the remainder of a farewell tour that began in May.

Cancellation of the final 24 concerts of the Tour 66 has prompted media speculation about the likely insurance impact of a move estimated to cost between 7 and 10 million euros, according to Hallyday's producer Jean-Claude Camus.