Had he had anything to eat/drink before you checked his crop?
What is Nimba doing that makes you think he's sick?
I would provide them with plenty of water to drink. Maybe soak their feed and see if that makes a difference.
Can you please tell us about his symptoms - you mention it seems like Flu? Does he cough, sneeze, have mucous coming from his nostril, trouble breathing, facial swelling, watery eyes or bubbles in the eyes?
Is his crop empty or full?
Can you provide any photos of what he looks like and of his...