Black Caps captain Kane Williamson had a solitary Plunket Shield knock for Northern Districts before taking a break to manage a hip injury.

New Zealand's top-six looks set in stone for the England cricket tests but two nagging questions leap out.

Can the Black Caps captain and key batsman Kane Williamson defy a niggly hip injury to play all five tests against England and Australia in the next two months, and who replaces him if he can't?

There appears some doubt over question one. Coach Gary Stead sounded more hopeful than bullish about his skipper's fitness as he and co-selector Gavin Larsen prepare to name their squad on Friday for next Thursday's first test at Mount Maunganui.

KAI SCHWOERER/GETTY IMAGES Coach Gary Stead and New Zealand captain Kane Williamson during the Plunket Shield opener last month in Christchurch.

"I hope so. You never know, injuries can happen. We just have to manage him well and make sure his stretching regimes and all those things are going to plan," Stead told Stuff.

READ MORE:

* Black Caps' Ashes blueprint

* England's emerging cricket star

* Ian Smith: NZ's non cheerleader

* Santner up to second in rankings

Interviewed during Sky TV's broadcast in Napier on Friday, Williamson described his hip injury as "an ongoing niggle", which restricted him to a solitary innings this season: 26 in 56 minutes for Northern Districts against Canterbury last month.

BUDDHIKA WEERASINGHE/GETTY IMAGES Kane Williamson led New Zealand to a 1-1 draw in Sri Lanka in August, their sixth unbeaten test series in a row.

"It comes and goes. It is settling, which is nice. A lot of [the last few months] has been rehab to get the hip right," he told Sky TV.

Having missed the five-match Twenty20 series as a precaution, Williamson goes in cold for five tough tests in just under seven weeks - two against England then three in Australia.

Interestingly, Stead said the longer Williamson bats, the less the injury bothers him. It appears diving or running in the field is the biggest concern as New Zealand hope to avoid the major setback of starting a test without their best player.

"It's not usually batting that aggravates it. Hopefully he bats for a long time and scores a lot of runs," Stead said.

"He's been with us the last couple of games and had a number of red ball trainings with us as well, getting back into the rhythm of playing. I'm reasonably confident he'll be OK come the first test."

It brings Otago batsman Hamish Rutherford into the frame for potentially his first test in nearly five years, as the leading backup option.

BRADLEY KANARIS/GETTY IMAGES Central Stags batsman Will Young scored a century against Australia in a warmup match in May before undergoing shoulder surgery.

Regular backup Will Young, still awaiting his test debut, remains sidelined until at least next month's Twenty20 Super Smash after undergoing shoulder surgery.

Another leading top-order contender, Wellington's South African run machine Devon Conway, doesn't qualify for New Zealand selection until September.

That leaves Rutherford who will open for New Zealand A in Friday's three-day tour match against England in Whangarei. Now 30, Rutherford scored a memorable 171 on debut against England in 2013 but played the last of his 16 tests in January 2015.

MARTY MELVILLE/PHOTOSPORT Otago's Hamish Rutherford is the likely next cab off the rank in the test top-order in case of injury or loss of form.

Rutherford scored 535 runs at 41 in last season's Plunket Shield, then averaged 44 in four County Championship matches for Worcestershire. This season Rutherford hasn't got into gear with scores of 22, 21 and 7 for Otago.

Again there's a glaring absence of quality young batsmen making big runs in first-class cricket, a worry for the selectors trying to formulate backup plans.

Even the form of the incumbents in the first three rounds of Plunket Shield gave cause for concern, notably opener Jeet Raval.

HAGEN HOPKINS/GETTY IMAGES It hasn't been a happy start to the season for test opener Jeet Raval, scoring 7, 3 and 14 for Auckland.

The left-hander who averages 34.64 from 20 tests - and will partner Tom Latham at the top - scored 37 runs in three innings in the 1-1 series draw with Sri Lanka, then for Auckland scored 7, 3 and 14.

In another frustration, Raval and Rutherford both missed out on much-needed innings when University Oval's poor drainage saw the Otago-Auckland game abandoned without a ball bowled.

Aside from Latham's 224 against Wellington, and Henry Nicholls' 103 against Northern Districts it was lean pickings for the Black Caps' batsmen, none of whom play for NZA this weekend while England's test lineup gets back-to-back warmup matches at Cobham Oval.

AT A GLANCE

Plunket Shield scores this season for the likely Black Caps test top-six:

Tom Latham (Canterbury): 20, 224, 23, 0

Jeet Raval (Auckland): 7, 3, 14

Kane Williamson (ND): 26

Ross Taylor (CD): 2, 18

Henry Nicholls (Canterbury) 103, 16, 15, 0

BJ Watling (ND): 2, 29, 44, 4, 21