Rookie hookers Liam Coltman or Nathan Harris are unlikely to be thrown into the fray against England next month unless they are absolutely ready to step up to Test level, All Blacks coach Steve Hansen said on Sunday.

Hansen has something of a hooking dilemma on his hands as he fine tunes his selections for next year's Rugby World Cup defence with veteran Keven Mealamu injury prone and understudy Dane Coles only 18 months into his test career.

He needs to blood at least one more hooker this year to build some depth there before the World Cup in England and has brought Coltman and Harris into an extended training squad for two three-day camps in Christchurch and Wellington.
"We think the two guys we have brought to the camp are two quality players and (they) are young men we're interested in,"

Hansen told reporters in Christchurch. "There's no rush for us to bring them in if we think they're not ready yet.
"History tells us that people step up and fill shoes when sometimes you don't think they're going to be able to.
"(But) you don't want to rush them in for the sake of it. They have to be ready to do it otherwise they're going to lose their confidence."
Hansen hinted he may only select two hookers in his 31-man squad for the three-test series against Stuart Lancaster's side that starts on 7 June in Auckland and if needed he had other options if injuries occurred.
"Obviously if we get injuries then Corey Flynn is not going overseas until after the Super (Rugby) competition so he could still be eligible," Hansen added of the 33-year-old World Cup winner, who was not included in the training squad and will join French club Toulouse later this year.
Hansen also said he would not be keen to spring too many surprise selections for the England series, despite naming five uncapped players in the extended squad.
"No," he said when asked if he saw the series as an opportunity to blood several new players and rest some of his veterans.
"The England series is going to be really tough and it's about picking the best 31 guys we can and getting their combinations out there and reacquainting ourselves so we can get our game structures and skill sets back up to the high level they were at last year."
Hansen added he was pleased to see Auckland Blues loose forward Jerome Kaino playing so well after two seasons in Japan, though the 48-test veteran was no guarantee to walk straight back into the side.
"It's exciting to see him come back and see him playing the way he is," Hansen said.
"He's going to have to prove himself again in test rugby if he gets the opportunity.
"He's an athlete that when he was at the top of his game he was the best in the world. Can he reach those levels again? We don't know but we're excited about finding out."