Tupou and the rest of the Wallabies front rowers were walking back to their hotel, the Sandton Sun, at approximately 9:15pm local after a dinner just across the road, when a man walked past and grabbed his phone before running towards a waiting vehicle.
After initially believing it to be one of his teammates, Tupou realised it was a stranger and pursued the man, sustaining some minor cuts to his arm attempting to grab the device out of the car.
Tupou said on Sunday evening (AEST) that he was feeling okay after the incident.
"Last night went out for dinner with the front rowers, it was just outside the hotel and I went back, someone came from behind and took my phone,' he said.
"I thought it was one of the boys so I looked back and he was wearing a hoodie and ran with my phone.
I tried to chase after him, he got in the car and I got a bit of a cut but I'm fine.
"The only thing is I lost my phone but I can live with that."
Tupou has been treated for the cuts but his injuries are not expected to hinder his chances of playing in Australia's their opening Rugby Championship Test against South Africa in six days' time.
Local police were contacted after the incident and took statements from all the players who were with Tupou but the 23-year-old was believed to be the only player involved in the incident.
Police believe the theft was part of a series of similar incidents.
The Wallabies only arrived in Johannesburg earlier on Saturday, after spending the first of two weeks in Africa at nearby Sun City.
Sandton is generally regarded as one of the safer districts in the South African capital but Tupou's experience has served to remind players of the risks of walking the streets late at night.
The Wallabies take on the Springboks in Johannesburg on Saturday July 20, kicking off at 5pm local,