Very sick Roo

[Poultry Showman]

Hi! There is something very wrong with my little roo here. I'm lost as to what to do because I can see that it's something internal. He had some green poo this morning and has recently been throwing up clear liquid. He has been abnormally still for some time. Up to three weeks. I have him situated in a towel because he is too weak to sit without falling over. He also has some water and food in front of him. He seems very hungry when I offer him food but appears to be barely able to keep his head up! He is a one year old cock, and has always been a very healthy chicken... until now! None of the other chickens have contracted it so I'm assuming that it's just a him thing. His name is Whip
Any help is appreciated!

Here are some pics.

Update: He is trying to twist his head as far as it can go to the right. So much so that he almost twists his body all the way over. What kind of sickness is this?

 

[Eggcessive]

How old is he? How does his crop feel—empty and flat, partly full, firm, doughy, or squishy? Has he been wormed recently? Do you have other roosters or hens in his flock that could have kept him from eating? What do you feed, and does he have grit available? Does he have any signs of a respiratory disease, such as bubbles in one eye, nasal drainage, or a swollen eyelid? Can you give him fluids that contain some electrolytes or sugar water? I would clean off his vent with a warm wet slightly soapy rag, but do not bathe him, as it could kill him. I would try to tube feed him fluids, and later some raw egg and plain yogurt. Aquarium air tubing or oxygen tubing trimmed to 12 inch length will fit a 35 ml feed store syringe for emergency tube feeding. Amazon sells proper baby lamb tubes and syringes. Here is a video on tube feeding:

 

[Poultry Showman]

No he's been eating fine up until now. He's just over one, and no respiratory diseases that I couldthink of. It's not Mareks because nothing is being paralyzed he is just weak and sick looking. Forgot to mention: I gave him electrolytes in his water about an hour ago and he is looking a little stronger. He can eat food on his own now without almost falling over completely.

 

[Poultry Showman]

Yes I did worm him.

 

[Eggcessive]

If you should lose him at some point, your state vet can do a necropsy and test for diseases if you keep the body in a cooler on ice. Here is a good link to keep to contact the state vet:
https://www.metzerfarms.com/poultry-labs.html

 

[Poultry Showman]

I wish I could but I can't afford to do that.