"On May 2, police were made aware of an incident at a supermarket in Papakura where a security guard was assaulted," he said.
"The victim was taken to Middlemore Hospital but sadly died in hospital early this morning from his injuries.
"Police have arrested a 17-year-old male in connection with the assault and our enquiries are ongoing.
"We cannot rule out the possibility of charges being laid."
Glossop said he could not comment further on the incident as the matter was before the courts.
"We are supporting the victim's family and our deepest sympathies are with them at this time," he said.
The victim's name has not been released.
It is understood police are still notifying his family overseas.
"We are deeply saddened by this tragic loss of one of our team," Countdown managing director Dave Chambers said.
"The safety of our people and customers is our absolute priority, and no New Zealander should go to work and not expect to return home to their loved ones.
"Our focus right now is to support the family and our team in whatever way we can.
"We've also made as much information and footage as we have available to the police and will continue to cooperate with their investigation."