The main thing to watch out for is zinc and magnesium levels. Make sure he has a good multi-vitamin, eats foods rich in zinc and magnesium (red meats for zinc, broccoli and oats for magnesium, and nuts/seeds for both), and get him to take some ZMA at night.
Charles Poliquin mentioned in an old article on here that he found that just about all of his atheletes at the time were zinc and/or magnesium depleted and some had been having trouble with conceiving a baby with their wives. Once he had them supplementing their performance in the gym and in the bedroom improved.
Also, I think the recommendation against a fat burner is probably a good one, especially if he was thinking of an over the counter one.
Finally, make sure he leaves at least a little saturated fat in his diet, and that he does not start cutting calories TOO deep. He does not want his T levels doing a sky dive.