Victoria Azarenka is set to miss the US Open because she is "not willing" to leave her child at home in California.
The Belarusian former world number one returned to tennis in June after giving birth to her son, Leo, in December.
Azarenka, 28, separated from his father in July and the pair are working "to resolve some of the legal processes".
In a statement, Azarenka said: "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."
The US Open will take place at Flushing Meadows from 28 August to 10 September.
Azarenka, Australian Open champion in 2012 and 2013, reached the final in New York in the same two years.
She was knocked out in the fourth round at Wimbledon this year. Last week, she pulled out of the Cincinnati Open because of "a family matter".
"Like most working mothers I am faced with a difficult situation which may not allow me to return to work right away," her statement added.
"Balancing childcare 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.
"I remain optimistic that in the coming days Leo's father and I can 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."