SBW's younger rivals for a spot in the centres are pushing him close. Photo: Juan Ignacio Roncoroni/EPA

WELLINGTON Sonny Bill Williams has enough credit in the bank to only need to prove his fitness to put himself into contention for his third Rugby World Cup later this year, All Blacks coach Steve Hansen has said.

The 33-year-old Auckland Blues back, a member of the World Cup winning squads in 2011 and 2015, suffered a knee injury in late March and had arthroscopic surgery.

It was the latest in a long list of injuries that have limited the inside centre's appearances since the last World Cup in England and questions were being asked if he would be able to make the All Blacks squad.

"I understand why people would say he's running out of time. But is he really?" Hansen told reporters in Auckland on Monday, adding that Williams was back running and would probably be available for the Blues again in two weeks.

"He's already proved himself. He's played 51 tests. That's a lot of test matches, that's a lot of proving.

"What we need to see is him getting back on the track. Then we've got to ask ourselves is his fitness good enough for him to be selected in the team?

"We play five test matches before we have to name the World Cup team, so does he deserve the opportunity to show us whether he's still good enough?

"Of course he does because he's played 50 test matches."

Hansen is likely to take just four midfield backs to Japan, with Williams, Ryan Crotty, Jack Goodhue, Anton Leinert-Brown and Ngani Laumape all in contention.

World Cup winner Ma'a Nonu, who last played for the All Blacks in the 2015 Rugby World Cup final victory over Australia, is also a dark horse selection after some strong performances for the Blues since he returned home from France.

Hansen added that other senior players like Ben Smith (hamstring), Owen Franks (shoulder), Dane Coles (calf) and Brodie Retallick (wrist) were progressing well in their recovery from injuries.

He was also pleased to see flanker Sam Cane make his return to the field last Saturday after he broke a bone in his neck against the Springboks seven months ago.

"He was excited about being back," Hansen said after Cane played about 41 minutes in the Waikato Chiefs 23-8 loss to the Blues on Saturday.

"When you get something taken away and you think you might not ever get it back again, when it comes back it's a real pleasure and joy. You can see that on his face." 

Reuters