imo, the other option is to say that his head wasn't right to face his old club and you don't want to risk a player who isn't completely 100% at this important stage of the season, or some crap like that. can't disprove it. personally, i reckon if there's a bunch of simple and hard-to-disprove ways around it then there's no point having the rule in the first place.
however: big sam is an utter tit for saying that was the case. why anyone ever employed him after the way his england stint ended is beyond me.