When you say a "crooked neck" chicken, how do you mean and can you post a photo of him? A twisted neck (wry neck) can be a symptom of several ailments, vitamin deficiency being the easiest one to fix, so a good poultry vitamin supplement like Nutri Drench would be a first step and a good quality all flock or grower with occasional scrambled egg or oily fish. A disease like Marek's is a likely candidate too if he is young, so isolating him from the rest of your flock might be a good idea if he has just arrived with you. It is a very common viral disease and easily transmitted to other chickens via inhaling dander dust from an infected bird and it is often fatal with no recognised treatment, so do consider taking precautions.
