Caroline Wozniacki's French Open preparations suffered a hit as she was forced to retire at the Internationaux de Strasbourg.
The former world number one and top seed was a set down to American Shelby Rogers in her opening match when she pulled out citing back trouble.
Wozniacki told wtatennis.com: "I felt it kind of in the middle of the first set. At this point, I think it's important for me to try and get ready for the French Open and be 100 per cent for that."
Rogers, the world number 55, won the one set played on a tie-break in just over an hour. She will now play China's Qiang Wang.
Second seed Elena Vesnina also went out after losing 1-6 6-1 6-1 to Camila Giorgi.
Fifth seed Caroline Garcia went through with a 6-3 6-4 victory over Jennifer Brady while seventh seed Daria Gavrilova beat Louisa Chirico 6-2 6-3.
Qualifier Elizaveta Kulichkova also progressed, beating Mandy Minella 6-1 6-4.
There was another an upset at the Versicherungs Cup in Nuremberg as third seed Zhang Shuai was beaten 6-7 6-3 6-4 in a two-hour tussle with France's Oceane Dodin.
Sixth seed and home favourite Julia Goerges saw off Nao Hibino 7-5 6-1.
Source: PA
