Poor baby. I'm posting a photo of a baby (found on a FB pigeon racing group) with a similar problem. Some members suggested piercing the crop with a small needle to let the air out. Others suggested this was a yeast infection. I still think you are dealing with yeast. The droppings show that little food is going through, almost looks like starvation droppings. What came out when you emptied the crop the first time? Formula?