The American was F1's chief doctor until the end of 2012, when president Jean Todt decided not to renew the contract.

Since then, he has been clinical professor of anaesthesia and emergency medicine at the university hospital in Liege, which last week reportedly received a visit from Gerard Saillant.

Working at the FIA Institute, Saillant is a mutual friend of both Todt and Michael Schumacher, and Hartstein claims it is he who fired him "by email" in 2012.

"Imagine my surprise to learn that despite having heard nothing from you or your boss (Todt) since being fired, you actually came to my hospital because of me!" Hartstein wrote in an open letter to Saillant and Todt on his blog.

On the blog, Hartstein has been a regular critic of the way the Schumacher camp handled the seven time world champion's public face of his skiing accident and injuries.

Last week, Hartstein was also critical of the FIA's investigation into the injuries sustained this year by Jules Bianchi.

Hartstein added: "You made an appointment with the Dean of my medical faculty, to speak about me. I'd be flattered if I wasn't so shocked.

"I think it's important that people understand just how you and your boss work," he added. "You came here to try to get me fired.

"You and your boss want me fired from the job that pays my rent. The one I've held for 25 years. Wow. Were you wearing a black trench coat and fedora?"

Hartstein said Saillant was armed for the meeting with the Dean with copies of his blog postings and also an email from Schumacher's wife Corinna.

"You came here to raise the issue of whether this blog violated my contract at work and could therefore be a reason to fire me, or at least to muzzle me," he added.

Hartstein defended his blog postings on the basis that they are his private opinions, based on nothing but "conjecture and experience".

"In fact, things like 'privacy' and 'free expression' come to mind - not as sterile principles, but as laws that you are on the cusp of violating," he raged.

"Be aware that I've referred the 'dossier' you handed over to the Dean to my attorney. You are on very, very thin legal ice.

"Word to the wise? Shut up, back off, and watch out," Hartstein concluded.