Wheelchair tennis' reigning US Open champion Lucas Sithole has been involved in an attempted carjacking in his native South Africa, where he and his brother were dragged out of their car by four armed men.

The national wheelchair federation says Sithole is "traumatized" but both brothers were unhurt in the incident on a highway onramp in Johannesburg late Friday night.

Wheelchair Tennis South Africa says the armed men jumped out of a vehicle in front of Sithole's, forced the men out of their car and stole their cellphones.

Sithole, 27, lost both his legs and his right arm in a train accident. He won the 2013 U.S. Open title.

South Africa's crime problem has been raised as an issue at the murder trial of double-amputee runner Oscar Pistorius, the country's most famous disabled sportsman.