Media outlets are being offered a medical file about Michael Schumacher's condition for at least EUR 50,000, Die Welt newspaper reported.
According to another major German daily, Bild-Zeitung, the great German's manager Sabine Kehm described the news as "horrifying and disgusting".
In a media statement, she said the medical documents, which cannot be authenticated, are nonetheless "clearly stolen. The theft has been reported. The authorities are involved.
"We expressly advise that both the purchase and the publication of such documents and data are forbidden," added Kehm, threatening to sue those who ignore her advice.
London's Times newspaper said the file has been offered to publications in the past days in Britain, Germany and France.