Need help on feeding a young finch bird.!!!?

My cat found a young bird, one of those small ones with brown feathers that are flying about constantly. About the same size as a Blue-tit. Anyway, couldn't find the nest, so I put it in the bushes nearby for about 5hours to see what would happen. It was still there. Perfectly fine, sent me on a wild-goose's chase trying to catch it. It drinks water from a small injection(without the needle), but I can't seem to get it to swallow any food. Its got some feathers. but its quite scrawny and either one of its wings or legs is wonky so it can't really fly very well. I don't know how old, but I would say its in the 'teenager' age... So what do i do now? I have it in a small box with sawdust cuttings, some food in a tiny bowl... and it keeps trying to get out. But I have cats everywhere, and if it can't fly, it sure as hell can't defend itself against a cat. Any tips what to do now? please!