ACT Brumbies lock Shawn Mackay died in a Durban hospital from a heart attack a week after suffering critical injuries when he was hit by a car, a spokesman for the team said on Monday.

Mackay, 26, had been in hospital with multiple injuries since the early hours of March 29.

"After his surgery Shawn contracted an infection in his bloodstream," Brumbies chief executive Andrew Fagan said. "He deteriorated rapidly and suffered a cardiac arrest from which he didn't recover."

Fagan said Mackay had shown some initial positive signs after being brought out of a medically induced coma late last week, but picked up an infection several days ago which was being treated with antibiotics.

"However, those antibiotics were failing to do the job and the doctors were unable to identify the source of the infection," he said, adding it led to a rapid deterioration of Mackay's condition in the last 12 hours.

"It's been a shock. It's devastating news for his family and for all of the Brumbies community," Fagan said. "Our thoughts and those of the players are with his family at this most difficult time."

Mackay had been admitted to St. Augustine's hospital in Durban with a cervical spinal fracture and dislocation, a fractured skull as well as a broken leg and multiple facial fractures after being struck by the vehicle on a Durban street.

The incident occurred about 4.15am Durban time when Mackay and a number of other Brumbies were leaving a nightclub after their Super 14 loss to the Sharks the previous evening.

Mackay's parents, John and Leonie Mackay, and girlfriend flew to South Africa last week to be by his side.

The Brumbies squad was flying back to Australia on Monday after completing a three-match trip to South Africa with a win over the Cheetahs in Bloemfontein last weekend. They were to be told of Mackay's death when they arrived back in Sydney off their international flight.

The Brumbies had signed Mackay, a former Australian 7s captain, to a one-year rookie contract for the 2009 season.

The backrower had six state caps for the New South Wales Waratahs and had been a member of the Australian Sevens side since 2004.

He also spent five years with the Sydney Roosters in the National Rugby League.

"I'm probably one of the older rookies going around but I'll be looking to draw on my experience to make the most of any opportunities I get at this level," Mackay said at the time of his signing with the Canberra-based Brumbies.

Born in Sydney, Mackay attended Waverley College alongside current Brumbies Stephen Hoiles and Patrick Phibbs. After leaving school Mackay played rugby league with the Roosters but in 2004 returned to rugby union.

Mackay played in two matches this Super 14 season, both on the South African tour. He came off the bench against the Lions in Johannesburg and against the Sharks the night before the accident.

Fagan said he wasn't sure how the team would cope with having to play South Africa's Stormers in Canberra on Saturday.

"I'm not sure at the moment how we're going to deal with that as a playing group," he said. "But they were able to rally for the game against the Cheetahs (last) weekend, with news that was difficult for them in dealing with Shawn's injuries in hospital.

"I expect they'll try and do their best again this weekend." The Australian Associated Press reported Monday that South African police had previously stated the driver of the vehicle which struck Mackay may be charged with reckless and negligent driving.

On Monday, a Brumbies spokesman said it was too early to know if more serious charges would now be laid.