Radebe announced he is to set up a trust in his wife's name to benefit cancer treatment centres in South Africa.
In a video message to press and supporters for the launch in South Africa, Radebe said on Leeds' official website: "Unfortunately the conference is about more than my testimonial. Just this week my wife Fezi has been diagnosed with, and is receiving treatment for, stomach cancer.
"As you know cancer is a serious illness, so her doctors are not taking any chances and I am confident she is receiving the best possible treatment. This is the reason why I am not there with you. I am sure you understand that at a difficult time like this she needs my support. Fezi's illness also means that we will have to postpone some of the events surrounding the testimonial match."