That tucked up and listless look is often coccidiosis and it can appear when chickens are bought and sold, as moving is a bit stressful, so it gives the bugs that were there chance to multiply. It could also be worms, who start causing problems for the same reason.
However, if it was coccidiosis, you'd expect to see him with watery poo or mucky feathers round his bum? What's his breathing like? Any rattle or bubbling round his nares?
Have you wormed them anyway, with them being new onto your place?