You can apply for an International Sportsperson visa if all of the following apply:
you’re an elite sportsperson or qualified coach, who’s recognised by your sport’s governing body as being at the highest level of your profession internationally
your sport’s governing body is endorsing your application
your employment will develop your sport in the UK at the highest level
you meet the other eligibility requirements.
On the international point, I don't know if the club can sponsor him to get around that point. Someone like Cust or even Mitch Pearce haven't represented Australia