1. You are on disability and working? Be careful. Working could jeopardize your disability
2. My suggestion is to quit that job and move on. I don't see the makings of a good lawsuit here.
3. If you were legitimately hurt, file a First Report of Work Injury with the Tennessee Department of Labor and ask the employer to provide medical care. Be prepared for that claim to be denied because right now, it will just look like sour grapes.
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As an "at will" employee, he unfortunately can treat you terribly. I would seriously suggest just getting another job
The information provided in this answer does not create an attorney-client relationship and is not considered to be legal advice.