My cat injured a bird. How to help an injured bird with no feathers?

Thanks for reaching out about this little bird. Often cat attacks are fatal for birds, as there are some pretty bad bacteria in the mouths and claws of cats. If this little bird is still in your possession, I would recommend contacting a wildlife rehabber in your area to see if they would be able to treat it with antibiotics and then rehabilitate it while its feathers grow back. Without its feathers, it makes it very difficult for birds to keep warm, even in warmer climates. If some of the tail feathers are missing, it can make it difficult for them to fly appropriately as well. To find wildlife rehabilitators in your area, you can search the NWRA website or the California wildlife rehabilitators group as well. Additionally, you may be able to contact a veterinarian who is comfortable seeing birds as they may have contacts for wildlife rehabilitators in the area as well.
I hope this gives you a place to start, and thank you for caring about this wild bird!