Serena Williams has revealed that she retired from her second-round match at the Wuhan Open because she was feeling "dizzy and nauseous".
The world number one was leading Alize Cornet 6-5 in the first set on Tuesday before she called for treatment at the side of the court.
Following some medical assistance, Williams then informed the umpire that she was unable to continue.
"I felt dizzy and nauseous in the first set and unfortunately couldn't continue," the 18-time Grand Slam champion said in a brief statement.
Williams suffered a similar incident at Wimbledon earlier this year when she was forced to retire from a doubles match after falling ill.