Serena Williams has revealed preparing for her return to tennis following the birth of her first child has been difficult and that she still has doubts about how she can "keep going".
Williams makes her comeback to the WTA Tour this week when she takes on Kazakhstan's Zarina Diyas in the opening round of the BNP Paribas Open in Indian Wells.
The 36-year-old was last in action 14 months ago when she clinched her 23rd grand slam singles title by winning the Australian Open.
She gave birth to daughter Alexis Olympia on September 1 and has since been working her way back to fitness.
"It's been hard," Williams said in an interview with BBC Sport. "There have been so many days, even still, that I'm like 'how am I going to keep going?'
"But I keep going and I know that I might not be at my best yet but I'm getting there. As long as I'm moving forward, even if it's at a turtle's pace, I'm OK with that."
Williams decided against defending her Australian Open crown in January following concerns over her ability to make an impact in Melbourne.
But she believes returning to singles action now - a month on from playing a Fed Cup doubles match for the USA - will stand her in good stead for the year's three remaining grand slams.
Speaking before competing at the Tiebreak Tens event in New York, where she reached the semi-finals, Williams added: "If I want to play in those grand slams and play well then now is the perfect time to start.
"My expectations, I don't know what they are. I can't go and say 'I expect to lose', because that's just something I'll never say. It's just a little different, I'm just expecting to see where I am more than anything.
"I don't need any more motivation, I have the best thing I could ever want right now. I've always been an extremely motivated person.
"My main thing is I would love for my daughter to be around with me doing great and playing amazing so it definitely gives me some motivation."