In a tribute piece written for the Guardian, Selvey says the former New Zealand cricket captain was sleeping 15 hours a day and using cannabis oil rather than undergoing more chemotherapy.
Selvey wrote that Crowe had told him this when the pair caught up in Auckland during last year's Cricket World Cup.
Selvey also says that at the time Crowe was given a 5% chance of living for a further year and that he was 13 days off that prognosis when he died yesterday, aged 53, of double hit lymphoma.
"He had been diagnosed with follicular lymphoma a couple of years previously but appeared to be in remission, cleared, until the cancer returned, in the virulent terminal form of double-hit lymphoma," he wrote.
"The apparently hale nature of his condition was a camouflage. When he was awake, he said, he did indeed feel good, but rather than undergoing yet more chemotherapy he was by then self-medicating with liquid marijuana and sleeping 15 hours a day. Happy hours though, he said."
Selvey added in his moving tribute: "Has there ever been a sharper cricket mind? Not in my experience. For all the orthodoxy of his play, he was an innovator, someone ahead of his time by years."
His article is among scores of tributes which have flooded in from around the world after the death of the Kiwi sporting great.
Medical marijuana use in New Zealand hit headlines again earlier this year when former union boss Helen Kelly sought legal and regular supply of the drug.
Ms Kelly, who has lung cancer, wrote to Associate Health Minister Peter Dunne in January to seek permission to use medicinal cannabis.
But earlier this month, the ministry responded to her application, saying it would be deferred because it did not contain enough information.
A spokesman for Mr Dunne told the New Zealand Herald the Ministry of Health was not aware of Crowe using the drug and there hadn't been any correspondence with him about it.
"No approach made to the minister or officials that we're aware of," the spokesman said.
"Not at all. It's news to us."
Mr Dunne was in Australia from Monday to Wednesday this week at the Australian Drug Foundation's National Drug Summit.
His spokesman said the minister was participating in a forum on the issue of medical marijuana and spoke with his ministerial counterparts in New South Wales and Canberra.
Australia recently passed legislation to legalise the cultivation of cannabis for medicinal purposes.
The legislation passed federal Parliament on Wednesday last week, and the Government is now expected to take at least six months to write the regulations to allow cannabis to be grown legally under licence.
Mr Dunne approved the use of medicinal cannabis for Nelson teenager Alex Renton last year. The 19-year-old, who suffered from seizures and was in a coma, died in July.
Last week Mr Dunne announced that the guidelines for considering applications from people wanting to use cannabis for medical purposes would be reviewed.
He said the need for "fine-tuning" was inevitable, given that medical cannabis was a new policy area for the Ministry of Health and wider medical profession.
"The guidelines were set up at my request following the Alex Renton case in 2015, so far the only case where ministerial approval was granted, following an application from Mr Renton's treating clinicians to administer the restricted product Elixinol," the minister said at the time.
He said the guidelines were more recently applied to an application for medical cannabis made on behalf of Ms Kelly, but subsequently withdrawn by her oncologist before any ministerial decision was required.
"While I am satisfied that on the whole the guidelines are sound, they were prepared as guidance only. They allow for flexibility across different clinical situations, and are certainly not set in stone as some have claimed.
"Nonetheless, some further review would be beneficial and I have asked officials to undertake further consideration of them. I am not ruling out seeking external input into this review process."
Ms Kelly was already using cannabis oil to ease her pain, and has said that the drug was "brilliant" for helping with nausea, lost appetite, and pain relief following chemotherapy.
Patients can apply to the Ministry of Health to get access to one form of medical cannabis, Sativex, which has been cleared for use in New Zealand.
Ms Kelly was seeking approval for a non-pharmaceutical-grade cannabis which does not have approval in New Zealand.
This has a stricter set of criteria for approval and requires the patient to be very ill or dying and in hospital when the treatment begins.
Ms Kelly resigned from the Council of Trade Unions in October because of her deteriorating condition.
