Current manager is leaving soon.

I'm working in a warehouse and my manager is about to leave in October. I'm starting to get afraid that they want to bring in an outside hire instead of promote me. It's their company so they can do whatever they like. They pay me well but I think I'll have a hard time teaching the new manager how to make more money than me and get all the credit for my work while I stay in the company shadows. I hope they make me the manager. Next week I'm going to bring this up with the company president.