It's 4 years continuous residence to become an Aussie citizen. But you also have to be a PR before you can apply. Basically he must have an Australian passport to be counted as an Aussie, so unless he has already got one (which you'd think he doesn't as we're having this debate) or has already applied and is likely to be accepted he's not an Aussie as far as the A-League is concerned. I think it is highly highly unlikely he will be anything but a foreign player.
BTW playing for another country has nothing to do with being classed as a foreigner in the A-League. It's completely about whether you're an Aussie citizen or not.