(CNN) -

Stolen medical files that may be those of Michael Schumacher are being offered for sale, the injured former F1 racing driver's manager said.

Schumacher has been undergoing hospital treatment since a skiing accident last year but is now out of a coma.

Manager Sabine Kehm said the documents had been offered for sale for several days.

She added, "We cannot judge if these documents are authentic. However, the documents are clearly stolen. The theft has been reported. The authorities are involved."

Medical files are confidential, and it is forbidden to buy or publish such data, Kehm said.

"We will therefore, in every single case, press for criminal charges and damages against any publication of the content or reference to the medical file," she said.

Schumacher, 45, suffered severe head trauma in a December 29 skiing accident at the French Alps resort of Meribel.

The champion driver, from Germany, was transferred last week to Switzerland for rehabilitation from a hospital in Grenoble, France, where he was kept in a medically induced coma for more than three months.

The Grenoble hospital's media office said in a statement that Kehm "told us that a person intended to sell to the press a document allegedly issued from the medical records of Michael Schumacher."

"Without knowing the precise nature of the document, the Grenoble Hospital decided to sue for 'theft and breach of medical confidentiality' so that an investigation can be initiated."

A spokesman for the German newspaper Bild, Tobias Frolich, told CNN that the tabloid was among a number of media outlets to be offered Schumacher's alleged medical records, but that "the editorial office decided to reject the offer."

A French prosecutor investigating the accident concluded that speed was not behind the fall suffered by the seven-time world champion, whose F1 career ended in 2012.