I would not place the chick in with any other birds with a wound of that significance - any bird, mum included, will pick at it and make it worse. If you think about it for a moment, this is how the injury came to be in the first place. You will want/need to brood this bird in a secure setting where it is not at risk of further damage from any other bird.
I would thoroughly clean the wound and go from there depending on what I saw (a picture once you have cleaned the wound would help)