New Zealand have been dealt a crushing World Cup blow after fly-half Dan Carter was ruled out of the rest of the tournament.

The 29-year-old suffered a groin injury during the All Blacks' final training session on Friday ahead of their Pool A clash against Canada in Wellington.

All Blacks team doctor Deb Robinson has now confirmed the extent of Carter's injury, which could have a damaging impact on New Zealand's quest to win a first world title since 1987.

Manawatu back Aaron Cruden has been called into the All Blacks World Cup squad by coach Graham Henry.

Carter, who has amassed a record 1250 points during his 85-cap Test career, had been due to captain New Zealand in their final pool fixture on Sunday.

Skipper Richie McCaw will rest a foot injury ahead of next weekend's probable quarter-final against Argentina, but leadership duties have now passed to hooker Andrew Hore, with Colin Slade wearing the number 10 shirt.

Carter, the world's leading fly-half, suffered the injury during a kicking drill at Wellington Regional Stadium.

He immediately slumped to the floor in agony, and the All Blacks' worst fears have now been realised.

Henry must now decide whether to persevere with Slade moving towards the tournament's knockout phase, or contemplate other options in the number 10 shirt such as versatile half-back Piri Weepu.

Robinson said a scan had shown Carter to have torn the adductor longus tendon in his left groin.

"The scan confirmed our worst fears that the tendon has torn, which means he is out of the tournament," she said.

And Henry added: "We are all obviously devastated for Daniel. He has worked so hard to be at a peak for Rugby World Cup.

"We will rally around him and pull together as a team."

Carter will now see a specialist to determine how the injury should be treated, with Robinson confirming that surgery was a possibility.

The All Blacks remain favourites to win the World Cup, although Carter's absence is likely to make that task considerably tougher than it might have been.