I had one that decided to stick it's whole fool head and neck out of it's pen and peck my hunter husky on the nose. The husky responded by ripping a quarter of the skin off of it's chest, right below the crop. It was around 3-4 weeks old.
I quarantined it with the smallest other chick (because it would NOT settle down while it was alone), restricted feed (because it's crop was trying to come out of the gap in it's skin if it ate too much) and treated the wound with some iodine for three days. It grew to be the second biggest bird of the lot. Not once did it ever act like an injured, sick, lame bird. I've found CX to be some of the most surprisingly hardy animals I have ever owned.
I always make the choice to treat based on condition. An animal that's alert, awake, and is actively trying to eat and drink with a good appetite is usually worth the effort to give it a week and see if it improves. It helps to always quarantine away from rougher, bullying chickens. An animal that's lethargic, sleeping a lot, not responding to fresh food/water, or is getting worse... I remove after 24-48 hours. The chances of it getting better are slim to none.