The thing is, the human body makes hCG. Everyone has it in their body. It's not like it only gets there if he injected it.
His level was elevated. From everything we've heard, it was elevated "slightly". That could possibly be from some medical condition. If that's the case, then he does need to find out how it happened and get that cleared up if possible. If he comes back with an actual medical condition that is treatable, then maybe he could get the suspension lifted.
IF he's telling the truth and he didn't inject it and he didn't ingest it, then there's not much else to say except that he's trying to figure out how/why the test came back positive and he's trying to figure out how to keep it from happening again.
IF he's NOT telling the truth, then he should know how to keep it from happening again.