The custody battle that's halting tennis pro Victoria Azarenka's career.

Two-time grand slam winner and former World number 1 Victoria Azarenka has announced she will not compete at the upcoming US Open due to an ongoing custody battle with her ex-partner.

“I am sadly unable to compete in this year’s US Open due to my ongoing family situation that I am working through,” Azarenka announced on Monday.

Sharing the news to Facebook, the 28-year-old wrote, "like most working mothers, despite my unconditional love for my son, I am faced with a difficult situation which may not allow me to return to work right away." 

She continued, "the way things stand now is that the only way I can play in the US Open this year is if I leave Leo behind in California, which I’m not willing to do."

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Azarenka welcomed her first child into the world in December last year and returned to competition in June. In July, the Belarussian announced she and her partner had separated.

Azarenka says she is "optimistic" that she and her ex-partner will be able to begin to work together to "put aside any differences and take steps in the right direction to more effectively work as a team and agree on an arrangement for all three of us to travel and for me to compete but, more importantly to ensure that Leo has a consistent presence from both of his parents."

Finally, Azarenka wrote, "Balancing child care and a career is not easy for any parent, but it is a challenge I am willing to face and embrace. I want to support men and women everywhere who know it is ok to be a working mother - or father. No one should ever have to decide between a child and their career, we are strong enough to do both."

It is not yet known when Azarenka will return to the court.