Chris Evert has been diagnosed with ovarian cancer and has begun chemotherapy, the American tennis great announced.

The 67-year-old Evert, whose on-court battles with Martina Navratilova in the 1970s and 1980s provided one of the greatest tennis rivalries, won 18 grand slam singles titles in a much-lauded career.

Evert told ESPN, for whom she has worked as a match analyst, that she underwent the first of six rounds of chemotherapy this week.

It means Evert has not travelled to Melbourne to work at the Australian Open, which begins on Monday. She said she would be providing analysis from home during the tournament.

The cancer was discovered after a preventive hysterectomy and Evert said it was found at an early stage.

In a message posted on Twitter, she said: "I wanted to share my stage 1 ovarian cancer diagnosis and the story behind it as a way to help others. I feel very lucky that they caught it early and expect positive results from my chemo plan."

Speaking to ESPN, she added: "I've lived a very charmed life. Now I have some challenges ahead of me. But, I have comfort in knowing the chemotherapy is to ensure that cancer does not come back.

"As someone who has always had control over my life, I have no idea how I'll respond to chemotherapy. I have to give in to something higher."

Evert's sister Jeanne died from ovarian cancer in February 2020.

"When I go into chemo, she is my inspiration," Evert added. "I'll be thinking of her. And she'll get me through it."

Messages of support poured in for Evert, with Navratilova writing: "We are all with you and behind you Chrissie, you are a true champion and I have no doubt you will conquer this nasty opponent with nary a sweat!"

Billie Jean King, a fellow American tennis legend, said she and her partner Ilana Kloss would have Evert "in our thoughts and prayers".

"Sending you so much love and healing thoughts, @ChrissieEvert ... and we wish you strength as you face this battle. You are one of a kind, and there are so many who love you," King said.

Among current WTA Tour stars, there were Twitter messages of support from the likes of Victoria Azarenka, Garbine Muguruza, Madison Keys, Paula Badosa and Ons Jabeur.

Tracy Austin, a fellow player-turned-analyst, told Evert: "You are one of the strongest people I know. There are so many of us that will be with you every step of the way."