King told The Associated Press that because of her mother's "failing health, I will not be able to join the U.S. Presidential delegation at this week's opening ceremonies of the Sochi Olympics."
Betty Moffitt, her 91-year-old mother, lives in Arizona and has been ill for some time. King will be joined by her brother Randy Moffitt, a former pitcher for the San Francisco Giants.
"It is important for me to be with my mother and my brother at this difficult time. I want to thank President Obama for including me in this historic mission and I look forward to supporting our athletes as they compete in Sochi."
The openly gay former tennis star has said she would like sexual orientation added to the list of protections in the charter of the International Olympic Committee. King was chosen in December for the U.S. delegation, along with openly gay former Olympic figure skater Brian Boitano and Cahow.
In June, Russia passed a law banning gay "propaganda" to minors. In an interview with the AP last month, King said: "It should be a non-issue. It's just like people of color in our country and other places, it has to be a non-issue."
President Barack Obama has been publicly critical of the Russian anti-gay law and President Vladimir Putin's "cold-war" mentality on other issues. For the first time since 2000, the U.S. delegation to the Olympics will not include a president, former president, vice president or first lady.
The 70-year-old King, a social justice trailblazer who won 39 Grand Slam titles in her career, was tapped to enter the fray involving the delicate balance of Olympic sports and politics.
Other members of the U.S. delegation for the opening ceremony include former Homeland Security Secretary Janet Napolitano, U.S. Ambassador to Russia Michael McFaul and presidential adviser Rob Nabors.
The White House statement said "The President extends his thoughts and prayers to Ms. King and her family in this difficult time."