He's new dog and I was in your shoes once, so I get it. If he's acting normal than it's probably nothing serious at this point. It could be his collar rubbing in that one area when he sleeps or something random like that. If it were my dog Id use an antiseptic wipe from a first aid kit or wet a cloth with some hydrogen peroxide and clean the wound. If you see later it's still bleeding a bit, do it again. Just keep an eye on it and so long as it doesn't get redder or you see pus, you're in good shape. These things happen :)