Johannesburg - Post mortem results reveal Vuyo Mbuli died of a pulmonary embolism.
The blood clot, which was found in his chest, caused a blockage in his lungs.
According to family spokesperson Rowena Baird, previous reports that the SABC radio and television presenter suffered a heart attack were false.
"His blood had clotted and he had two relatively large clots," she told the broadcaster. "The clots tend to move around the body, and they moved to his chest, hence he complained of chest pains," she added.
The 46-year-old broadcaster collapsed while watching the Cheetahs' 27-13 Vodacom Super Rugby win over the Reds at the Free State Stadium on Saturday night.
He was treated on the scene before being taken to the Mediclinic hospital in Bloemfontein, where he died.
South Africans will have an opportunity to bid farewell to Vuyo Mbuli.
The broadcasting icon's memorial service at SABC's Renaissance Hall in Auckland Park tomorrow afternoon will be open to the public.