Might not have been weak or ill. Could have been young, stupid, distracted, inexperienced, or just slower than the others or closer to the perimeter. But still not a good idea to eat it unless it was a very fresh kill, IMO.
Hmm. I think the Bible has something to say about this, but off the top of my head I can't remember. I think it says not to eat anything that dies of itself or that is torn in the field. I'll look it up. I believe an animal killed by a predator, that dies in terror, is flushed with adrenaline...