Sonny Bill Williams must work for World Cup spot if he returns to New Zealand

The New Zealand Rugby Union would welcome the return of Sonny Bill Williams, but there is no guarantee he would be included in World Cup plans.

Williams won the World Cup with the All Blacks in 2011 then the Super Rugby title with the Waikato Chiefs in 2012, but he rejoined rugby league this year, moving to Sydney Roosters in Australia's National Rugby League.

A switch back to Union could be on the cards for Williams, with reports suggesting he will come back to New Zealand in a bid to claim a 2015 World Cup spot, but he will not receive special treatment from the NZRU.

"The coaching staff and contracting team work very hard to have positive exit relationship with all our players and coaches," said NZRU chief executive Steve Tew.

"The door stays open and we communicate with them on a regular basis. But they know the rule, if you're not in the country then you can't be an All Black.

"If you want to come back then the door is always open.

"In Sonny's case, he's the same as everyone else. If he comes back fantastic. If he doesn't we respect that."