Today I went out to my aviary to find one of my baby gouldian finches on the ground. I noticed its right wing was damaged and upon closer inspection I was shocked to find the most part of its wing chopped completely off at the bone. I tried looking for a stray piece of wing as horrible as that sounds but to no avail. Not sure if it was a cat but I've never had a problem with birds getting attacked by wild animals in the past five years.
Anyway, the baby bird seems okay and isn't too frightened at all really, but it cant fly to the latter part of the cage to be with other birds and get food. Thankfully I had water on the ground earlier for the birds. I am not sure what to do with the bird and I think if I segregate it from the rest he might get restless and under shock... I only have experience with budgies. Anyway, any advice on what to do here? The bird is currently staying inside with me

Thanks in advance