Simona Halep withdrew from her second-round match at the WTA Cincinnati Masters on Wednesday due to a right thigh injury she suffered at the US Open hardcourt tuneup event.
The fifth seed from Romania was to have faced American Jessica Pegula but pulled out after hurting herself in the previous round in a victory over Poland's Magda Linette.
"After feeling a sharp pain in my right adductor during the match yesterday, I called the physio and, with heavy taping, was able to carry on and win." Halep said.
"Unfortunately, a scan this morning showed that I have a small tear in the adductor and, therefore, it would be too risky for me to play this evening.
"I will rest up and do everything I can to be ready for the US Open. To the fans in Cincy, it was beautiful to see you again."
Pegula earned a walkover into the third round.
Halep is just back on court after another injury in Rome last May that kept her from Roland Garros, Wimbledon and the Olympics.