If you were treated differently from the other general manager based on your membership in some protected class--such as, race, gender, age, religion, etc.--then, you might have a claim, for discrimination, against your employer. Best of luck to you.
Employers are allowed to treat their employees differently unless the reason for the different treatment is unlawful. Employers can play favorites, look the other way with some employees they like more than others, and fire one employee and give a verbal warning to another for the exact same conduct. Only if the reason for the different treatment is because you are a member of a protected class of people or because you had engaged in legally-protected conduct would there be a potential case for unlawful discrimination.
In short, discrimination is not unlawful. Most forms of discrimination never give rise to a claim. Only a very narrow kind of discrimination is unlawful.
Good luck to you.
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Mr Pedersen's answer is spot on. Many people use the term "discrimination" in a way the law does not mean it. Discrimination is only *illegal* if it is based on what is called a protected characteristic (race, age, sex, or disability, among others) or a protected act (complaining about something *illegal*).
You don't say in your post why you "believe it's discrimination." Your belief isn't enough to make a case. Nor is it enough to demonstrate that you have a protected characteristic different than the other manager. There may be many reasons why you were demoted and the other person wasn't. The protected characteristic may give you an indication that illegal discrimination is going on, but it wouldn't be proof of it.
I hope this information is helpful to you.
Craig T. Byrnes
Disclaimer: Please be aware that I am not offering legal advice, nor forming an attorney-client relationship with you. I am not representing you, nor doing anything to protect your legal rights. If you believe that you have suffered a legal wrong, take action before any statute or limitations expires, or your right to do so may be lost forever. Good luck in your legal matter.