You are not permitted to download, save or email this image. Visit image gallery to purchase the image.
The 72-year-old, who played 104 times for Otago and 30 matches for the national side in the mid-1970s, was seen by a passing motorist near the gate of his Hunter Rd, Dalefield, home about 9pm on Sunday.
He was flown to Christchurch Hospital with head and chest injuries.
Sergeant Simon Matheson, of Queenstown, said Mr Robertson had been outside chopping wood and doing other tasks before he took a wheelie bin out to the road.
He remembered walking back, stopping to have a rest and "after that, not a whole lot more".
"He remembers there being cars, but whether one hit him he doesn't know.
"We're still trying to determine whether a vehicle was involved or if it was a medical event."
It was possible a vehicle had narrowly missed him, causing him to fall.
He had been wearing dark-coloured clothing on an unlit road with an 80kmh speed limit.
Mr Robertson was likely to remain in hospital today and tomorrow, and would be undergoing medical tests, Sgt Matheson said.
He had not been interviewed by police yet, he said.
Sgt Matheson said it was initially feared Mr Robertson had suffered a fractured skull, but tests showed that not to be the case.
His condition was listed as stable yesterday, and his family were hopeful he would be allowed to return home soon.
He would be interviewed by police after having some time to recover.
Police were "very thankful" to the female motorist who had seen him and gone to his aid, and wanted to hear from anyone else who was in the Hunter Rd or Mooney Rd area about 9pm on Sunday.
In a social media post yesterday, his daughter Olivia said it was suspected her father had been hit by a car.
"Any information of a friend or family member that has arrived home last night with suspicious damage to their vehicle, then we ask you to please inform police.
"And if you are the person that left my father, an elderly man lying unconscious and bleeding out in the middle of the road, then shame on you ... and please we ask you to turn yourself in."
Mr Robertson represented the All Blacks from 1974 to 1977, either at first five-eighth or fullback. He played many of his games for Otago at second-five-eighth.
-Police (03) 441-1600, Crimestoppers 0800 555 111