That injury certainly looks like quail on quail violence. In my experience it is usually roos fighting, but I have a trio of hens that did that to a new male that I tried to introduce to them.
You can try to do a bachelor pen, but if they're already fighting, the will probably continue to do so. The one that gets injured is either less dominant or weaker than the other. It's hard to say.
Be careful of putting just one hen in with a roo. He will likely overbreed her and might cause injuries in his enthusiasm. 3-5 hens would be better.