Sonny Bill Williams will wear the All Blacks jersey twice more this year in back-to-back Bledisloe Cup matches against Australia, before leaving New Zealand rugby.

The New Zealand Rugby Union is quietly negotiating with Japanese club Panasonic Wild Knights to allow Williams to take on Robbie Deans' Wallabies.

The Wild Knights wanted the superstar midfielder to take a three-week break before he joins them in September for a 12-game stint said to be worth $1.7 million.

But the Sunday Star-Times understands the Chiefs second five-eighths has made himself available for the two Bledisloe Cup tests in Sydney and Auckland on August 18 and 25, subject to his Japanese club agreeing.

All Blacks' management will select Williams on the basis that the best available players should be chosen to meet Australia. The reality is that Williams' blockbusting form this season has been too compelling to overlook.

The tests against the Wallabies are set to be his swansong from New Zealand, provided he gets approval from the Wild Knights. After his stint in Japan, he is then expected return to rugby league with the Sydney Roosters next year, continuing his code-hopping exploits.

Williams is understood to be excited over the opportunity to again play for the All Blacks and the NZRU will help smooth the way with his Japanese club. With experienced centre Conrad Smith to be sidelined for six weeks after eye surgery and Richard Kahui out after shoulder surgery, Williams' presence has become increasingly important to the All Blacks' depleted midfield stocks.

It's understood Williams will be selected purely as a No 12, ruling out a possible call up for Crusaders second-five Ryan Crotty and the Hurricanes' Tim Bateman. A combination where Ma'a Nonu shifts out to centre is being strongly considered. Highlanders utility Ben Smith could also play centre and team-mate Tamati Ellison is another midfield option.

Williams' name will not be announced in the All Blacks training squad tomorrow. Chiefs players are exempt from next week's two-day camp in Wellington as they prepare for their Super Rugby final, to be staged in either Hamilton or Cape Town next weekend, depending on the overnight result between the Stormers and Sharks.

The 26-year-old's addition to the All Blacks 28-man Rugby Championship squad, which will be unveiled next Sunday, will polarise public opinion, with sections believing he should not be given the chance to add to his 17 caps after announcing intentions to move in a different direction. However, Williams has received the backing of All Blacks team-mates, including captain Richie McCaw.

“If he's available, you saw the way he played tonight. If he's keen and it all works well I don't see that being a problem to be honest,” McCaw said after the Crusaders' season ended on Friday night.

“Losing a guy like Conrad who is very experienced, having Sonny available, he's got some experience now, it would be positive.”

All Blacks playmaker Dan Carter echoed those views. “They are pretty important matches first up. It'd be great to have him in the team. If he's available and can play it would be huge for us, especially with Conrad being out.”

- © Fairfax NZ News