Serena Williams has revealed she felt like she was "not a good mom" and was "in a funk" before pulling out of the Rogers Cup in Montreal.
The Wimbledon runner-up withdrew from the tournament on Saturday citing "personal reasons".
Earlier in the week she had suffered the worst defeat of her professional career in San Jose when she won just a single game against Johanna Konta.
In an Instagram post on Monday, Williams described her experience of tackling the challenges of motherhood while seeking further glory.
She wrote: "Last week was not easy for me. Not only was I accepting some tough personal stuff, but I just was in a funk. Mostly, I felt like I was not a good mom."
Williams, who suffered life-threatening complications after the birth of daughter Alexis Olympia Ohanian Jr, highlighted how "postpartum emotions" can continue for several years.
She explained that, after discussing her emotions with family and friends, she was reassured "that my feelings are totally normal".
Expressing empathy with other mothers, Williams said: "It's totally normal to feel like I'm not doing enough for my baby.
"We have all been there. I work a lot, I train, and I'm trying to be the best athlete I can be.
"However, that means although I have been with her every day of her life, I'm not around as much as I would like to be.
"Most of you moms deal with the same thing. Whether stay-at-home or working, finding that balance with kids is a true art. You are the true heroes."
Williams returned to tennis earlier this year after giving birth in September 2017.
The 23-time grand slam winner looked to add to her tally before being defeated by Angelique Kerber in the Wimbledon final in July.
Willams stressed at the time that there was nothing normal about her being back in a slam final so soon after childbirth and the life-threatening complications that followed.
She said after the final: "I have so much to look forward to and I'm literally just getting started."