Sanders, who was just 46, was shot in the hand and stomach.
Thieves charged into the eatery near Brits in the north of the city, and Sanders was struck. He later died in hospital, according to reports on South African station News24.
The Pretoria southpaw, full name Cornelius, shocked the world in 2003 with a spectacular two-round knockout victory over Wladimir Klitschko.
CORRIE SANDERS CHAMPION
At the time, he claimed the WBO heavyweight belt. Sanders went on to fight older brother Vitali a year later, losing in eight rounds.
The Klitschko brothers released a statement expressing their sadness.
“We were shocked to learn of the sudden death of Corrie Sanders, and we want to express our sincere condolences to his family,” the pair said.
“We will remember Corrie as a great person both inside and outside the ring.
“He was a great fighter with a big heart who always positively represented the sport of boxing.”
He retired in 2008 with a record of 42-4 with 31 stoppages after almost 20 years in the sport.
Corrie Sanders will be sorely missed by the boxing community, who have now lost another one of its fighting warriors in tragic circumstances.