It was probably born with something that made it harder to thrive - might have been a long hatch, temp might have not been ideal for whatever reason. I don't think falling would cause slow growth, but I am no expert.
I had one this season who was not doing well at all. She would lie on her side panting. She couldn't walk or anything. I nursed her back by taking her inside and using a dropper to give her water and feed her egg yolk every half hour for 2-3 days. I kept her extra warm on a heating pad or carried her with me in a pouch with hand warmers inside. She is doing great now. But if you are concerned that this chick might not make it, you might consider intervening and brooding it yourself.