Serena Williams has revealed preparing for her return to tennis following the birth of her first child has been difficult.

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 hopes returning to action now will stand her in good stead for the year's three remaining grand slams, adding: "If I want to play in those grand slams and play well then now is the perfect time to start."