As Olivia Newton-John battles cancer for the third time, she's reportedly become worried about her family.

According to an insider, she's asked her close friend John Travolta to look after her only child Chloe Lattanzi if her health takes a turn for the worst.

"The hardest thing for Olivia isn't the thought of dying but leaving Chloe behind, fragile and virtually alone in the world. This causes her the most grief and torment," a family friend tells Woman's Day.

"She bought Chloe the farm she and her fiance James [Driskill] live on and has set her up financially but she wants to make sure she has emotional support, too."

The insider says that Travolta knows what Newton-John is going through more than anyone.

"John loves and admires Olivia for the way she's battled this disease, and she's given him the hope and encouragement he needs," the source spills.

"Olivia has always been deeply concerned about who would look out for Chloe if she wasn't around. She's asked John to pledge to be that person. He didn't blink an eye and said, 'Of course.'"

This is due to Travolta, 66, losing his wife Kelly Preston to stage four breast cancer back in July.