One day after hinting that her retirement is drawing near, Serena Williams shed further light on the subject with a first-person essay published in the latest issue of Vogue magazine.

“It’s the hardest thing that I could ever imagine,” she wrote. “I don’t want it to be over, but at the same time I’m ready for what’s next.”

The 23-time Grand Slam singles champion, stopped short of saying the upcoming US Open would be her final tournament.

The essay, with the title “The Hardest Thing,” was revealed on ABC’s “Good Morning America.”

“[There’s] no happiness in this topic for me,” she wrote. “The best word to describe what I’m up to is evolution. I’m here to tell you that I’m evolving away from tennis, toward other things that are important to me.”

Serena Williams: Bio, matches and more

Williams, 40, concedes the subject of walking away from tennis is not a happy one, but says she is content with her achievements.

"Over the years, I hope that people come to think of me as symbolizing something bigger than tennis," Williams writes. "I admire Billie Jean [King] because she transcended her sport. I'd like it to be: Serena is this and she's that and she was a great tennis player and she won those Slams."

On Monday, Williams defeated Nuria Parrizas-Diaz 6-3, 6-4 at the National Bank Open. It was her first victory in more than 14 months.

“I love playing though, so it’s like amazing,” she said. “But, you know, I can’t do this forever. I guess there’s just a light at the end of the tunnel.”

Perhaps the biggest piece of news to emerge was Williams’ desire to have another child with husband Alexis Ohanian. When her daughter Alexis Olympia Ohanian, Jr., was born nearly five years ago, Williams suffered life-threatening complications.

“In the last year, Alexis and I have been trying to have another child, and we recently got some information from my doctor that put my mind at ease and made me feel that whenever we're ready, we can add to our family,” Serena wrote. “I definitely don’t want to be pregnant again as an athlete. I need to be two feet into tennis or two feet out.

Watch this: Serena's sizzling winner earns standing ovation

“These days, if I have to choose between building my tennis résumé and building my family, I choose the latter.”

After the win in Toronto, Serena said this was the first time her daughter had been courtside for a match.

“I looked over and I saw her in the first middle of the first set and I was like, `Oh, my God, why is she here?’ And then I went into mom mode, like, does she have on her sun cream?

“But I was like, 'OK Serena, just let go and enjoy this.’ It was good for her to have that memory. And I was like really happy. And then I was like, ‘OK, no racquet smashing. Stay calm.’”

Serena Williams stretches for a forehand during her quarterfinal win over Simona Halep.

Tennis Australia/Natasha Morello

Serena, like her older sister Venus, has already created a large footprint beyond tennis. Her investment company Serena Ventures has made significant investments in startups Tonal, MasterClass and Noom, among others. SV launched earlier this year with a $111 early-stage venture capital fund -- with 78 percent of their companies’ portfolios founded by women or people of color.

Williams next plays the winner between Belinda Bencic and Tereza Martincova. Williams’ previous outing was a loss in a third-set tiebreak at Wimbledon to Harmony Tan.

“Unfortunately I wasn’t ready to win Wimbledon this year,” Williams wrote. “And I don’t know if I will be ready to win New York. But I’m going to try. And the lead-up tournaments will be fun. 

Williams admitted she is not seeking to end her career with a final, ceremonial moment but to express gratitude.

“I’m terrible at goodbyes, the world’s worst. But please know that I am more grateful for you than I can ever express in words. You have carried me to so many wins and so many trophies. I’m going to miss that version of me, that girl who played tennis. And I’m going to miss you.”