"I sent him a message saying, 'I know you can get through this,' and, 'Don't listen to stage 4 and all of [that]. Don't read the statistics and stay focused and see how you can heal yourself,'" Newton-John, 70, told Entertainment Tonight on Monday.
"That helps. Sense of humor is vital," she added of the beloved TV personality. "He has a great attitude and a great sense of humor about it and I'm sure he'll do very well."
Trebek, 78, revealed last week that he was diagnosed with stage 4 pancreatic cancer.
"Now normally, the prognosis for this is not very encouraging, but I’m going to fight this, and I’m going to keep working," he said. "And with the love and support of my family and friends and with the help of your prayers also, I plan to beat the low survival rate statistics for this disease."
"Truth told, I have to! Because under the terms of my contract, I have to host 'Jeopardy!' for three more years!" he added. "So help me. Keep the faith and we’ll win. We’ll get it done. Thank you."
Newton-John beat breast cancer in 1992, but the disease returned in May 2017 in the form of a tumor on her shoulder. In September 2018, she revealed she had a tumor on her lower spine, which made it difficult for her to walk — a skill she had to secretly re-learn in the hospital, Newton-John said.
“Nobody knew I was there, so I was undercover boss in the hospital — on purpose,” the "Physical" singer told Entertainment Tonight. “I didn’t want people to know because I didn’t want it to be out there in the public that I was in the hospital. I was learning how to walk again. I was using a walker, so I’d wear a beanie and glasses and masks, so no one would know who I was.”
Fox News' Elizabeth Zwirz contributed to this report.