The Czech–American is considered one of the greatest players of all time. She says she will fight the disease "with all have I got."
Martina Navratilova said she had been diagnosed with throat and breast cancer.
In a statement released Monday, the tennis legend said her prognosis was good, and she would start treatment this month.
"This double whammy is serious but still fixable, and I'm hoping for a favorable outcome," the 66-year-old Navratilova said.
"It's going to stink for a while, but I'll fight with all have I got."
The cancer was discovered in early November during the WTA finals when Navratilova noticed a swelling in her neck that did not go down and had biopsies performed.
Navratilova battled cancer before
Navratilova underwent treatment for breast cancer in 2010 and was later declared cancer-free.
She originally retired from tennis in 1994 but later returned to the tour to play doubles in 2000 and occasionally competed in singles. She won 59 Grand Slam titles overall, including 31 in women's doubles and 10 in mixed doubles.
More recently, she worked as a television analyst.
Because of her latest diagnosis, she would not be a regular part of Tennis Channel's coverage of the Australian Open but would appear from time to time remotely.
Fellow tennis star take to social media to offer support
Navratilova took to Twitter to "thank you all for your support, and I am not done yet,'' she tweeted Monday.
Among her well-wishers was another tennis trailblazer Billie Jean King.
"Martina is as brave as she is strong," King wrote on Twitter. "She has fought this battle before, and she is in our thoughts and prayers."
Chris Evert, Navratilova's great rival on the courts who became her friend, revealed in January 2022 that she had ovarian cancer but was declared to be in remission in May.
She wrote on Twitter that Navratilova "is a woman who takes on challenges with strength and resilience…You got this, Martina!"