Serena Williams says she is suffering from "postpartum emotions" as the 23-time Grand Slam winner struggles to deal with juggling family life and tennis.
The 36-year-old American is seeking to regain her top form after missing most of the 2017 WTA season due to a pregnancy.
"I read several articles that said postpartum emotions can last up to three years if not dealt with," Williams said on Monday.
Williams' disclosure comes a week after she suffered the worst loss of her career in San Jose, losing the final 12 games in a shocking 6-1, 6-0 first-round upset to unseeded Johanna Konta.
On Monday, she described her mindset at the time as being in a "funk".
"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 wrote on her social media Instagram account.
Williams said she is trying to work through her despair by sharing her feelings with family and friends.
"Talking things through with my mom, my sisters, my friends let me know that my feelings are totally normal. It's totally normal to feel like I'm not doing enough for my baby .... Whether stay-at-home or working, finding that balance with kids is a true art," she said.
Organizers announced on Saturday that Williams was withdrawing from this week's WTA Montreal tournament citing "personal reasons".
Williams battled back from life-saving surgery after giving birth to daughter Olympia in September, reaching the final at Wimbledon, where she was beaten by Germany's Angelique Kerber.
Williams had a tough draw in Montreal. Her opening match would have been against Frenchwoman Alize Cornet who has defeated Williams four out of the six times they have faced each other.
If she advanced past Cornet, her next opponent would have been Kerber.