Serena Williams is expecting a baby and will not play again in 2017, her representative has confirmed.
The 23-time grand slam singles champion hinted at a pregnancy when she posted a picture of herself in a yellow swimsuit, showing off a prominent bump, on the social media app Snapchat.
It came with the caption "20 weeks", but was then deleted without explanation before official confirmation came several hours later.
A short statement from her representative on Wednesday (Thursday AEST) said: "I'm happy to confirm Serena is expecting a baby this Fall."
Williams, who will return to the Tour in 2018, won the Australian Open in January and was pregnant at the time of that success, if she is now at the 20-week stage.
She announced her engagement to Reddit co-founder Alexis Ohanian in December and has not played on tour since her grand slam success in Australia when she overtook Steffi Graf to claim the outright Open era record for slam singles titles.
She pulled out of the recent tournaments in Indian Wells and Miami citing a knee injury but was scheduled to play at the Madrid Open next month.
The 35-year-old will return to world No.1 on Monday despite her recent inaction, though that stay at the summit will now not last for long.
Williams has made no secret of her desire to have a family.
Speaking to Glamour magazine last year, she said: "I definitely want to have kids one day.
"That's always something I've wanted as long as I could remember. And the older I get, the more I'm like, 'I'm too young!'.
"Hopefully I'll be able to mature one of these days, get serious, and at least have them pretty fast."
Williams will be the second top player in less than a year to take time away from the tour to have a baby.
Former world No.1 Victoria Azarenka gave birth to her first child Leo on December 20 and is planning to return to the sport at the Bank of the West Classic in Stanford at the end of July.
Williams' apparent announcement quickly became big news. The United States Tennis Association sent its congratulations.
The USTA stated on Twitter: "The GOAT (greatest of all time) herself @serenawilliams took to Snapchat to announce she's 20 weeks pregnant! Congratulations Serena!"
Accompanied by a picture of Williams with the trophy, a message on the US Open account read: ".@serenawilliams will have a new pride & joy to hug and call her own soon! Congratulations on the exciting baby announcement! #USOpen"