Albert Bojone was attacked by a lion on Tuesday but was not seriously hurt, said spokesperson Henritte Engelbrecht.
He broke a thumb and was recovering at a clinic in Upington.
Bojone and two other men were on the Botswana side of the park and planning to catch and bring back three local Kalahari lions that had slipped over the border.
One of the lions had caught a cow and was shot dead by a farmer. The other two were also eventually put down by parks personnel as they had become extremely aggressive.
Lions 'extremely aggressive'
Explained Engelbrecht in a telephone interview:
"Part of (a ranger's) conservation duty is to keep track of our lions. A certain area of the Botswana side (of the transfrontier park) is not fenced at all and animals move freely from South Africa to Botswana."
The three predators formed one group. Rangers believed they belonged to the same pride.
"They were like brothers but were extremely aggressive. It could be that they don't see people often, or they were traumatised ... by seeing the other lion shot," said Engelbrecht.
Bojone, an experienced ranger, was standing on the back of a pick-up truck and his two colleagues were seated in the front of the vehicle as they approached the surviving big cats.
Suddenly one of the lions jumped onto the bakkie.
"It grabbed [Bojone's] arm but then the lion lost a little control and fell back. Bojone then jumped and scrambled to get onto the roof of the bakkie," according to Engelbrecht.
The cat then grabbed at Bojone's foot.
"He tried to kick the lion off him ..."
Researcher Graeme Ellis, seated in front of the vehicle, scrambled out and went to help.
"He risked his life and pulled Bojone out of the jaws of the lion and pulled him into the [cab of the] bakkie."
The lion had a firm grip and "Bojone was pulled out of his boot ..."
When the attacker was shot dead, it still had the boot in its jaw, said Engelbrecht.
The third lion also had to be shot dead as it was aggressive.
Rangers' usual technique in handling lion attacks on vehicles is to toss a blanket on the beast.
"They would normally fight with the blanket and then get tired and give up," Engelbrecht said."