All Black swansong for Sonny Bill?

Sonny Bill Williams may make an unexpected swansong for the world champion All Blacks in the Rugby Championship following Conrad Smith's injury.

Williams was believed to be out of contention for the All Blacks following his announcement earlier this month that he had signed for a stint in Japanese club rugby and then planned to return to Australia's National Rugby League.

New Zealand Rugby Union (NZRU) chief Tew said selectors were considering the 26-year-old because Smith had been sidelined for six weeks after eye surgery for a detached retina, ruling him out of the opening matches of the Rugby Championship.

Richard Kahui is also out injured, leaving the All Blacks short of midfield experience for the opening matches of the tournament against arch-rivals Australia.

Tew said that could open the door for Williams, whose New Zealand rugby career was expected to end some time in the next fortnight, depending on how far his team the Waikato Chiefs go in the Super Rugby finals.

"He's eligible under our selection policy because he's been playing in the competition prior to the team being selected," Tew told reporters.

"I guess the conversation will be whether he has time to play in the competition before he goes to Japan."

Williams is tipped to earn in excess of $1.4 million during his stint in Japan with club side Panasonic and a further $570,000 in the NRL.

He is yet to reveal which NRL team he will play for, although reports say he is set to join Bondi-based glamour club the Sydney Roosters.