It would have been inconceivable to many four years ago that two time World Player of the Year Dan Carter would have to prove himself ahead of a World Cup, but All Blacks coach Steve Hansen insists rugby's leading points scorer has had to earn his place.

The 33-year-old had been under immense pressure from younger rivals to perform at test level after an underwhelming two years.

That pressure was never more evident in July when Lima Sopoaga delivered a strong performance on his debut against South Africa in the All Blacks' late 27-20 win at Ellis Park.

Carter then looked pedestrian against Australia in New Zealand's 27-19 loss in Sydney earlier this month and pundits began to question whether time and a series of leg injuries had caught up with him.

"The guy that was probably under the most pressure at that point was Daniel [Carter]," Hansen said in reference to Sopoaga's emergence this season as a genuine contender, along with Beauden Barrett and Colin Slade, for the number 10 jersey.

Carter responded from the disappointment of Sydney with a big game the following week at Eden Park, with signs that his running game was returning.

"He came out ... and played his best test match in a number of years against Australia and was telling us he's back in form," Hansen added.

"His running of the game was great and we had established that Dan was the man we wanted to take, with the uniqueness of the rules of the tournament."

It is appropriate Hansen mentioned the rules of the tournament given what happened to Carter at the last World Cup.

An automatic choice in the All Blacks starting line-up, Carter tore his groin while practicing goal kicking ahead of their final pool game.

According to World Cup regulations, if a team opts to call in a replacement to the squad then the injured player must sit out the remainder of the tournament.

Questions were raised as to whether New Zealand could win the title without Carter but fourth-choice fly-half Stephen Donald came into the side after more injuries and slotted the penalty that gave them an 8-7 win over France in the final.

Hansen has therefore opted for the versatility of Barrett and Slade to accompany Carter to England. Both are specialist fly-halves but can also cover fullback and, at a pinch, wing as well.

While Sopoaga did not make the squad for the World Cup, Hansen believed he would be more than ready to handle the pressure if the occasion called.

"The good thing is that if we do have to call him up, we now know that ... he's not going to be having his first game for the All Blacks," Hansen added.

"He's coming in confident that he's been in an environment - Ellis Park is as good as it gets, against the Boks - and we are comfortable he can cope with it; his team are comfortable he can cope with it and he'll be comfortable he can cope with it."