Injured baby cockerel

My 13-15 week old cockerel can't stand up/walk and i am so worried! when he does walk (extremely rare) he drags his leg like it isn't attached to his body, i am worried that he has either dislocated or broken his leg ...He is in with 5 hens and one other cockerel which doesn't attack him btw...the cockerels are quite alright together and he wasn't born like that so i am wondering if he may have had an injury of some kind, like he may have fallen of the perch and fallen in some kind or slipped on the floor. what can i do to help him? please help me! i have got really attached to these chicks and i would be devastated if he was to die! thanks in advance

Deep breath.
Yes, it would seem apparent that he has suffered some sort of injury - the first step is going to be to ID the type of injury, this will better enable you to decide on a good course of treatment and give you a better idea of the prognosis. Pick the bird up and hold him securely - manipulate the bad leg to identify any obvious breaks or abnormalities. If you don't feel an obvious break or find an obvious wound your next step is to assess the range of motion of the good leg and then go back and do the same with the bad leg, this can help you to feel problems that are not as obvious as a broken bone, etc such as misaligned internal structures.
If you are not able to identify the issue yourself after this you may need to seek help from either someone more experienced or, if it's an option for you, a veterinarian.
In the meantime, keep the bird in a "hospital pen" that provides him a safe space (an injured bird knows it is at risk of attack due to being less mobile than it's healthy flockmates and this alone causes distress in the animal) where he can comfortably rest (bed it deeply since he will spend most of his time laying down and to provide padding if he stumbles/falls while trying to move about) and easily access food/water. Keep the bird hydrated (soaking the feed can help with this) and provide good supportive care. This is key whether you have to provide other repair (ie splinting etc depending on the injury you diagnose) or if he is simply in need of time to allow his body to heal itself (ie soft tissue damage,etc)

Thanks for the advice! we are going to take him to get checked over hopefully tomorrow! i hope he is ok xxx