I just discovered that my cat has an open cyst on his low back near his tail on the right side. I know he was in a cat fight yesterday, and very well may have been attacked from behind. The wound is like a small crater and has a deep opening with a slight green ball of mucus that smells like a dead animal in it. It is almost 10:30 at night; can he wait until the early a.m. to be taken to the vet?