Rugby World Cup-winning coach Graham Henry has revealed what he considers to be the All Blacks' biggest weakness ahead of this year's tournament in Japan.

Henry, who led the Kiwis to the 2011 title after the disappointment of the 2007 quarter-final exit to France, told Newstalk ZB's Jim Kayes the season-ending injury of Chiefs utility back Damian McKenzie would be a sensitive blow to the team's hopes of a World Cup threepeat - but wouldn't be their main concern.

Instead, Steve Hansen should be trying to find a world-class blindside flanker, with injuries and inconsistent form having stymied several candidates' claims on the No 6 jersey in the post-Jerome Kaino era.

"If you look at the All Blacks right now, they're obviously going to miss Damian but the only other position is probably six, where they haven't really found Jerome Kaino's replacement," Henry said.

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"So they've been fiddling around with that position and I think they will sort that out before the Rugby World Cup - who is that person. But in every other position apart from the McKenzie injury, they're looking in pretty good shape."

Liam Squire has had a horror run with injuries this season. Photo / Photosport
Liam Squire has had a horror run with injuries this season. Photo / Photosport

While the Highlanders' Liam Squire was seemingly leading the race as recently as late last year, serious hip and knee injuries have kept the destructive runner sidelined the entire season - and facing at least another month off the pitch.

Squire's form in the last few tests of 2018 wasn't great and he's just signed a contract with a Japanese club for 2020 which won't preclude him from being selected for the World Cup, but could become a factor in a close decision.

While the departures of Jackson Hemopo and Jordan Taufua to overseas clubs effectively rules them out of selection, Shannon Frizell, Vaea Fifita and the fast emerging Tom Robinson are all genuinely in the frame.

Frizell is the closest in style to Kaino, the 83-test veteran who signed for Toulouse in France last year, but his lack of top-level experience remains a concern.

Henry, one of the most successful coaches in history, suggested the All Blacks take a closer look at Crusaders lock Scott Barrett, who has impressed on the side of the scrum over the past 18 months.

"If you put the best eight forwards on the park, he may be [one of them]. When you've got Brodie Retallick and Sam Whitelock who are probably as good as any locking pair in the world, it might be a position.

"He's certainly got the catch-pass skills to play six? Has he got the running ability and the big hit defensively? I guess that's the question. He's a hell of a good player and he's played superbly over the last 18 months.

Scott Barrett could be an option for the All Blacks at blindside, according to Graham Henry. Photo / Photosport
Scott Barrett could be an option for the All Blacks at blindside, according to Graham Henry. Photo / Photosport

"[Liam Squire] just seems to get injured a lot ... He needs a run, doesn't he? He needs a run of time where he can cement himself back in the team...

"He's got the big bang defensively and he carries with aggression and he's a hard man to knock over. So he could be the answer but I think that is certainly a question mark in the selectors' minds at the moment - number six."

The All Blacks face South Africa, Canada, Namibia and Italy in pool play in Japan, with the first match against the Boks on 21 September.