Serena Williams says she frequently wondered how she would keep going after returning to the practice courts following the birth of her first child.
The 23-time Grand Slam singles champion will return to the WTA Tour at Indian Wells in California this week.
In an interview with BBC Sport, the 36-year-old American said she is motivated by the thought of playing long enough for her six-month-old daughter to have memories of watching her.
“It’s been hard,” she said.
“There have been so many days, even still, when I’m like, ‘how am I going to keep going?’
“It’s been really, really difficult but I keep going and I know that I might not be at my best yet, but I’m getting there and every day is a new day and every day I should be getting better.
“As long as I’m moving forward, even if it’s at a turtle’s pace, then I’m OK with that.”
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Williams was speaking before competing at the Tiebreak Tens event at New York’s Madison Square Garden.
In an article for CNN last month, she wrote she feels “lucky to have survived” Alexis Olympia’s birth, having suffered a pulmonary embolism after an emergency Caesarean section.
“I’m ready, or else I wouldn’t be here,” she said.
“If I’m not ready now, I’m just never going to be ready. I feel in two months I’ll be way better than I am now, but you have to start somewhere. I don’t want to keep sitting on the sidelines and thinking about it.”
Williams can take encouragement from her performance in New York on Monday. Her serve looked threatening and she hit some menacing winners as she beat another returning player – Marion Bartoli – before losing to Zhang Shuai in the semi-finals.
Williams last appeared in a Grand Slam at the 2017 Australian Open. Victory over sister Venus in the final left her just one behind Margaret Court’s all-time record of 24 Grand Slam singles titles.
She has made no secret of the fact she is motivated by the thought of winning 25. And also by giving her daughter a meaningful chance to watch her play.
“I don’t need any more motivation,” Williams said.
“I have the best thing I could ever want right now. I’ve always been an extremely motivated person, but my main thing is that I would love for my daughter to be around with me doing great, and playing amazing, so that definitely gives me some motivation.
“I would have thought I would have retired six years ago, but I’m still here and I’m playing great, and I think I’ll still be playing good.”
She added it was “impossible” to say how long she would continue to play for.
Williams, who is unranked as she has spent more than 12 months away from the tour, has been drawn to play Zarina Diyas of Kazakhstan in the first round in Indian Wells. The match is likely to be played on Thursday evening, Californian time.
She could play her sister Venus in the third round, but has understandably sounded a note of caution.
After all, the former world number one only gave birth six months ago, and six weeks of that time was spent in bed as she recovered from emergency surgery.
“My expectations, I don’t know what they are,” said Williams.
“I can’t go and say I expect to lose because that is something I will never say. It’s just a little different. I’m just expecting to see where I am more than anything.
“This is a good time to start for the summer. If I want to play in those Grand Slams [the French Open, Wimbledon and the US Open] and play well, I think now is the perfect time to start.”
The only mother to have won the Wimbledon singles title since World War One was Australia’s Evonne Cawley (nee Goolagong) in 1980.
Another motivating factor, should Williams ever need one.