The tennis star revealed yesterday that a routine mammogram in February had uncovered the disease, though the cancer is believed to be localised and her prognosis has been described as "excellent".
Speaking to ABC's Good Morning America, Navratilova said: "I found out on February 24, it was my personal 9/11. I was devastated. Physically I could not think or move, I was useless. The emotions took so much physical strength out of me.
"At first I thought I would keep it private and that there was no need to talk about it. But the more I found out about what it was, I thought, 'This is ridiculous'. I am a healthy person, I am a health and fitness ambassador. I have been healthy all my life and all of a sudden I have cancer. Are you kidding me?"
She added: "But I took four years before I had my last mammogram, I let it slide. I moved, I changed doctors and I thought I would get to it. I didn't realise it had been four years. I want to encourage women to have that yearly check-up.
"I am lucky that this DCIS [Ductal carcinoma in situ] started in the last year. If it had started before I would have been in deep trouble. I would have needed chemotherapy. The cancer would have spread. But it is just in one breast and I will be okay."