The Love Story star was diagnosed with stage-two prostate cancer in early April (12), but he assured fans his prognosis was positive and he was expected to make a full recovery.
On Monday, the actor was slated to open up about his relationship with tragic lover Farrah Fawcett in a candid chat with Today show host Matt Lauer, but the heavily-promoted segment had to be postponed after the 71 year old fell sick.
Informing viewers of the schedule change, Lauer said, "We are sad to say Mr. O'Neal showed up here this morning... he was not feeling well. He has since gone back to his hotel and we are told he is cancelling all of his appearances for today. We hope he is all right, and we hope to see him tomorrow morning, here on Today."
The actor fought leukaemia in the late 1990s and he also reportedly has a skin cancer spot on his nose.