Catt with yellow leaf - Need Advice

[ardera]

So when I got this Catt, there were some yellow leaves on it. The nursery staff told me "Catts don't mind getting sunburned, they will bounce back". However one of the leaves that was yellow has only gotten worse. Attached are some pics, and I am wondering if I should remove the leaf, as it seems to be getting so much worse. There are also some black spots, that might not be from sunburn? The spot on the side of the leaf, seems to be getting larger too, leaf had been damaged there. Do/should I just remove the leaf, remove the whole pbulb, or what should I do?