A foot problem forced French Open winner Garbine Muguruza to retire, with the fifth seed lasting less than 30 minutes on Tuesday to exit her opening match at the Dubai Tennis Championships.
Opponent Kateryna Bondarenko earned a 4-1 win in 24 minutes, with Muguruza visited by the trainer after a quarter of an hour.
The Spaniard was not particularly clear in her mind as to exactly what her problem was, dismissing an ankle diagnosis from the physio and instead saying it was her left Achilles tendon which was the worry.
"I have been training but on and off, honestly, because of the pain," she said.
"Some days it was a little bit better, some days it was a little bit worse. It was just hard for me to serve, especially, and to just move side to side today on the court."
The 2015 semi-finalist picked up the injury last week in Doha.
"I don't think it's like something big, hopefully, but it's very irritated and it's really bothering me every time I have to run on the court," she said.
Russian Ekaterina Makarova scored another upset as she put out third seed Dominika Cibulkova 6-2, 4-6, 6-2.
The victory over the Slovak was the second in as many months for Makarova, also a winner in the third round of the Australian Open against Cibulkova.
"Beating her at the Open helped a lot, I was believing more and I knew what to do, how to play, where to go, yeah, I was believing that I can beat her," Makarova said.
Cibulkova took the third seeding behind Angelique Kerber and Karolina Pliskova.
The 2012 champion Agnieszka Radwanska reached the third round after a bye, beating Belgian Dubai debutante Elise Mertens 6-3, 6-2.
Eighth seed Elena Vesnina defeated Misaki Doi 6-2, 7-5, Olympic champion Monica Puig stopped 5th seed Caroline Garcia 6-1, 4-6, 6-2, while Croatian Ana Konjuh accounted for 12th-seeded Australian veteran Samantha Stosur 6-4, 6-3.
A trio of Americans all advanced with wins for Catherine Bellis, Christina McHale and Lauren Davis.
