we just adopted another cat, this will be our 5th. He has been neutered and dewormed during the last two weeks, he is still in the process of introduction to our older cats, after two nasty fights he engaged with the old male, we decided to keep him in a different area of the house so that they won't have any more chance to fight. However, after a week of their last fight we notice that he's got a big bump on his head near the ear. Now it is leaking. Our vet will come to check on him tomorrow morning, so until then I was wondering if you have any ideas of what could it be this bump and how to treat it.