Strydom told television channel eNCA that he fought off the attackers, but was left with cuts on his head and a fracture to his skull and jaw.
He said that he was attacked Monday in the South African capital Pretoria when he saw a person lying on the road and stopped his car, thinking they needed help. He said the attackers then threw bricks at his car, with one smashing his window and hitting him in the head.
The people tried to steal his car, but he fought them off and drove himself to the hospital, he said.
"I remember I was standing there surrounded by six people and I had to fight for my life," the six-foot-six former second-rower said.
Strydom was a member of the Springboks' famed 1995 World Cup-winning team.
Violent carjackings are common in South Africa, which struggles with high levels of crime. Strydom was the second well-known sportsman to become a victim of crime in recent months.
South African national soccer team captain Senzo Meyiwa was shot to death in an apparent house robbery in October.
Police are still searching for his killers.