There are a range of options that could be placed on the table, from walking away on top now to playing all scheduled cricket for a finite period. The end result will almost certainly fall between those two extremes.
"We would like some certainty around that, but the natural time for that to happen would be at the end of the contracting period, which is in July," Crocker said.
That is also when McCullum finishes a seven-game stint with English T20 franchise the Birmingham Bears.
McCullum's partnership with head coach Mike Hesson has transformed the Black Caps from a team written off as overpaid and under-achieving, to a national treasure that last month galvanised the wider public with their run to the World Cup final.
New Zealand has always been competitive in limited overs cricket, however, so it really has been in the test arena that the upswing has been most marked. In 2014, New Zealand won five tests, including three away, making it their most successful calendar year on record.
With high-profile series on the radar against England (away) and Australia (home and away), it is a trend they desperately want to continue. With more power being thrust into the hands of the self-styled Big Three - Australia, India and England - it is vital New Zealand remain competitive to ensure regular bilateral series with the powerbrokers.
McCullum made his one-day debut in 2002 and his test debut two years later. He hung up the gloves in tests in 2010 to extend his career, by his reckoning, for another four to five years. The hard-hitting batsman who has become renowned for throwing himself around in the field is feeling the effects of 13 years on the international circuit and would like to spend more time with wife Ellissa and their three children, as well as devote more time to business interests including Vermair Racing, a thoroughbred bloodstock venture.
In recent days, he has been coy about his future plans but it is believed retirement after the tour to England - two tests, five ODIs and a T20 - is an option being seriously considered.
NZC is hoping the lure of 100 consecutive tests will convince McCullum to stick around. It would be a remarkable feat for a New Zealander and one that could also be highly marketable for the NZC commercial team.
With 92 consecutive tests, McCullum has smashed Stephen Fleming's New Zealand record of 72 and is the third-highest active player behind England's Alastair Cook (107) and South Africa's AB de Villiers (98), and ninth overall. Vettori's 113 tests is the New Zealand record, although he missed several matches through injury.
To get to 100, McCullum would need to play England, three tests in Australia before Christmas, two at home to Sri Lanka and then Australia at home to end New Zealand's home international programme next summer.
To increase the chance of that, the Herald on Sunday understands McCullum will be given the option to skip the limited-overs only tours to Zimbabwe and South Africa in August-September, and home ODIs against Sri Lanka and Pakistan.
It is unclear whether McCullum has any appetite for the World T20 in India, which follows the home summer and precedes the 2016 IPL.
Another factor is that McCullum is almost certain to be in a high-stress situation in October, when he will most likely be called on to testify against Chris Cairns in London's High Court when the former New Zealand allrounder faces perjury charges.
