Him being ill might be totally unrelated to eating the chappie. If he has been ill for a week, it would be best to take him to the vet, especially in hot weather, as he could easily get dehydrated.

With regard to him eating usually, it is best to never 'tempt' him if you can help it. Put his food down, if he hasn't eaten it after say, 20 mins, pick it up again and he doesn't get fed until his next meal. If he is hungry, he will eat.