All you can do is try, but to increase your chances of success, put them all in a pen that is new or unfamiliar for a week or so before reintroducing them to their home pen, do it in the dark when they cannot see well. This will help prevent the others from viewing the "newcomer" as a threat.
I just re read your post, I thought you said it was injured on its head, you did not. sometimes a hen can get rejected for reasons unknown to me.
but I would try to confirm absolutely the sex, usually with hens you just don't have much trouble.
Are you certain they're all hens?
I think you might have a bloodied rooster, With the whites its hard to tell.
and yeah I had one barely injured but the blood got everywhere, looked like a cardinal.