Serena Williams says she pulled out of this week's Rogers Cup in Canada after feeling like she was "in a funk" and "not a good mom".
The American 23-time Grand Slam singles champion initially withdrew from the tournament citing "personal reasons".
Williams, 36, returned to tennis earlier this year after giving birth in September 2017.
She reached the Wimbledon final in July but last week suffered the heaviest defeat of her career.
Williams' 6-1 6-0 loss to Britain's Johanna Konta at the Silicon Valley Classic event was the first time since turning professional in 1995 that she had failed to win at least two games in a match.