A German man, arrested in France after his wife said he held her captive for 12 years, will be released on Tuesday without charges, the lead prosecutor in the case said.

Police arrested the 55-year old on Monday after his wife was found naked in a poor state following what she said was captivity at the couple's home since 2011.

But her husband denied this, saying that his wife had cancer and that he was caring for her.

Prosecutor Olivier Glady said Tuesday there was "no evidence" that would justify a continued investigation into the man.

"The kidnap scenario never happened," he said.

Forensic medicine examination of the man's wife, a 53-year-old Spanish-German national, had also failed to produce any signs of rape or injuries, the prosecutor said.

Doubts about the wife's narrative had emerged already on Monday, when doctors found no broken bones or bruises as they examined her.

Her accounts to investigators meanwhile contained "inconsistencies", police said.

Prosecutor Glady had predicted on Monday that "the cursor is probably moving away from a scenario of horror, towards unsatisfactory conditions of the care of a sick person".

The man would be released by Tuesday evening, he said.