Is it Mareks??

[yellowblack]

 

[rebrascora]

That chick looks quite young for Marek's which typically strikes between 8weeks and 12 months although there are always exceptions.

I would try a vitamin supplement and see if that helps.

 

[Eggcessive]

I agree, the chick is too young for Mareks symptoms. A slipped tendon or other leg bone deformity is possible, but I would treat with poultry vitamins in the water right away. Make sure it contains riboflavin.
http://www.thepoultrysite.com/articles/1051/leg-health-in-large-broilers/
https://www.researchgate.net/public..._of_the_intertarsal_joint_in_broiler_chickens