Former world number one Serena Williams has explained why she retired from her third-round match at Indian Wells in California, USA.
The 23-time Grand Slam champion retired while trailing Spanish player Garbine Muguruza 6-3 1-0 on Sunday.
Williams took to the court for the second set, but the 37-year-old retired after Muguruza held in the opening game.
"Before the match I did not feel great and then it just got worse with every second - extreme dizziness and extreme fatigue," Williams said on BBC.
"By the score it might have looked like I started well, but I was not feeling at all well physically. I will focus on getting better and start preparing for Miami (Open)."
Muguruza is now set to face Dutch player Kiki Bertens, who defeated Britain's Johanna Konta.
Williams was eliminated from the first Grand Slam tournament of the year, Australian Open in the quarter-finals two months ago.
She will be hoping to recover before the upcoming French Open which will start in May 2019.