Poor dear He looks dreadful.

If you feel really desperate, especially if you get to the vet and he is going to die or is having grim outlook, you could try force feeding..

I did this with a frog who, although in much better shape than yours, refused to eat, and he lived a number of years more with me. I used silkworms, they are pretty good for sick herps in my opinion.

Worth a try, but don't stress him out...otherwise, just get him to the vet.