sorry thats a clock shop i should have said c**k shop, nevermind i'm sure they will put a couple of hands on it
to be serious, most sexual disease take longer to appear, herpes symtons are blisters, but these usually appear after a rash, syphillus too appears as an ulcer or sore, but this take 2-3 weeks, if he abstained for a few weeks before he's probably ok its just an bit of friction, i've had bruising there before, which is common, anyway its always best to be safe than sorry, and get it checked out
ps, my knowledge is not peronal experiance, just naval experiance