All Blacks gambling on fitness of injured star for Rugby World Cup

Retallick was forced off the field midway through the opening half of Saturday's Bledisloe Cup encounter in Dunedin with a knee injury with Tupou Vaa'i coming on to replace him.

Both players have been included in New Zealand's World Cup squad along with Sam Whitelock and Scott Barrett as the three-time world champions' four locks for the global showpiece in France.

However, All Blacks medical staff have assessed Retallick's injury and ruled him out for six weeks with the World Cup's start just under five weeks away.

"We're not 100 per cent sure whether (his return) will be round one, round two of the World Cup," Foster told AAP.

"But we really believe that he's earned his selection and can manage that."

The All Blacks squad announcement was made in Napier, home of the New Zealand National Provincial Championship (NPC) outfit the Hawke's Bay Magpies where Retallick plays his provincial rugby.

There was plenty of concern in New Zealand over Retallick's fitness when he left the field in Dunedin against the Wallabies and when his name was read out at the World Cup squad announcement, he received the biggest roar of all the All Blacks players.

"Maybe because I'm the only one from Hawke's Bay," he joked.

"It's not ideal timing and yes it's a little bit sore," he said of his injury, which will keep him on the sidelines for the tournament opener against host nation France.

"Hopefully I'll be available for the second pool game. I'll miss maybe two games, three at worst. I have to follow their plan and hope that it goes to the timeline."

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