If no injury has happened to the leg, I would lean to it being splayed!
Splayed legs are caused from either not enough nesting material, poor diet or parents can sometimes sit too hard on their chicks. Mostly though, it is through insuficiant nesting material.
I see by your photo that there is not much nesting material in the nest box. Chicks need plenty of material to grip onto so their legs don't go from underneath them and end up splayed. The bare floor does not supply this as they can't grip and their leg/legs can grow similar to the splits. If the parents keep kicking out the bedding, keep replacing it.
Not sure if there is alot that you can do. Depends on how long the little one has been like this for. I have read of a few "home" remedies but not sure how reliable these work or how safe they are for the chick, so I won't repeat them.
Hopefully someone here has had experience with splayed legs or knows of something that might make him a little more comfortable.
Let us know how you go.
