To be honest, there is no deep math in game theory. The most important thing is the idea of strategic thinking. The only thing to be learnt is about how to model certain agents with certain strategies. There is already some norms in this field, and that is the reason why we need to learn game theory, i.e. to learn the conventions and norms how to write models, or how to discuss a problem in the approach and language of game theory.
Anyway, the math needed for game theory I can think of is as following: optimization method, fundamental probability theory, fundamental calculus. That's it.