Greg LeMond -- a 3-time Tour de France champion -- just revealed he's been diagnosed with chronic myelogenous leukemia ... a treatable form of cancer.
60-year-old LeMond -- who is considered one of the greatest cyclists ever -- said in a statement he was concerned about his health after weeks of fatigue ... so he went to see his doctor.
"Following a series of tests and a bone marrow biopsy, which was completed last week, I received my formal diagnosis last Friday," the cyclist revealed.