Defamation is publically (i.e. to any third parties; that is, to any person not you) making negative factual statements (so not negative opinions or negative true facts, but negative lies or untruths about facts) which damage your reputation. Telling your coworkers that you have faked injuries and claiming that you are in an abusive domestic relationship--assuming that these things are not true--would seem to be defamation. Based on what you write, you may therefore have a defamation claim against your manager personally and possibly against your employer as well (if the employer is aware of his acts, which are being ostensibly done for the company's benefit [i.e. to fight your worker's comp claim] and, even though aware of them, let's him continue doing this). It would be worth your while to consult with a personal injury attorney about this situation in detail; many such attorneys will provide a free initial consultation, and you can inquire into this before making the appointment. Do not call from a company phone, or use a company phone, computer, server, network, etc. to email or text the lawyer--companies can, to greater and lesser degrees, monitory communications over their equipment or facilities.