The dog, Homebush Milo, died after winning a race.
Homebush Milo was the fourth greyhound to die at a race since Racing Minister Winston Peters announced in December that a ban would be brought in.
The chief executive of Greyhound Racing New Zealand, Edward Rennell, said the dog died suddenly, and had no visible injuries.
"Clearly there has been a medical event. I think last year we had four dogs die suddenly when racing out of just over 36 thousand starters, so it is a rare event.
"When it does happen we will get an autopsy done to determine if there was any factors in it."
He said in addition to the four dogs that died suddenly in the last year, nine had to be euthanised after a race.
Rennell said such events were unfortunate, but happened in all forms of racing.
SAFE (Save Animals From Exploitation) campaign manager Emma Brodie said Homebush Milo's death was another tragic reminder of why greyhound racing had no future.
"Homebush Milo should have had a life beyond the track but instead, like so many before him, he paid the ultimate price for an industry designed to fail him," Brodie said.
She said despite the upcoming ban, with racing due to end in July 2026, Greyhound Racing NZ (GRNZ) continued to put dogs in harm's way instead of preparing for the inevitable.
"They should be working on winding down races, transitioning workers out of the industry, and ensuring every greyhound is rehabilitated and rehomed into loving families."
She said SAFE was calling on GRNZ to "accept reality" that racing was coming to an end.
"The government has drawn a line in the sand, so GRNZ has two choices: spend the next 18 months racing dogs to death or focus on what really matters - giving greyhounds the future they deserve."
