Hallyday had an operation overnight on Wednesday to Thursday at LA's Cedars Sinai hospital to fix lingering back trouble from a Nov 26 operation in Paris - led by Dr Delajoux - for a herniated disc.
Hallyday's press service said on Thursday that lesions from the initial operation required more surgery, and that he had suffered an infection following the first operation.
Mr Camus told France's TF1 television on Friday that Hallyday was put in a coma "so he won't suffer," and the outlook was positive.
"The news is very positive, he's very strong," the rocker's son David Hallyday, himself a singer, told France-Info radio as he arrived at the hospital late on Friday.
Mr Camus, speaking Friday on French radio, said the American medical team treating Hallyday said the rocker had suffered ill-effects from the operation in France, and that infection "was attacking his bone marrow".
"If what I'm being told in the United States is true, this operation was a massacre," he said on RTL radio. On France-Info, Camus said: "It seems the Americans fixed things that they found that were very badly done."