ERROR Code says bad catalyst

[whitey]

My check engine light came on and i took my car to autozone and advance auto, their code checker came up with, bad catalyst left bank!so im thinking its either a bad O2 sensor or clogged cat. My friend who also has a 240 says that their is 2 O2 sensors behind the cat. I would like to know if i can remove my cat and not mess up the readings for those 2 sensors. I just bought the car so im not to familiar with it.its a 95 240sx