My cat is not eating?

  So I got two cats. One of them I got a week ago, then sent to hospital because he was sick. During the time he was at hospital, we got our second cat, which we’ve only had for four days. Our second cat is an oriental shorthair so I’m assuming they’re naturally thin, so we didn’t worry about it at first. He’s really shy, and runs away whenever we approach him. We tried placing him next to the cat food but he still won’t. There’s nothing in the litter box. So my mum made him some chicken, which he ate only a tiny bit of.

  The next day, our first cat came back, and he stopped eating again. Even chicken.

  The two cats fight frequently so I’m guessing they hate each other? My first cat eats anything I give him, like he’s always hungry.

  Is it because my second cat’s mad about first cat being here? Is he depressed or what?