Opening her Dubai campaign against Kateryna Bondarenko, Muguruza called a medical timeout after losing the first three games of the match and then retired two games later, trailing 1-4. Bondarenko will play either Caroline Wozniacki or Viktorija Golubic in the third round.
Muguruza told reporters the injury is a new one. She began to feel the pain after her last match at the Qatar Total Open last week.
"When I finished in Doha, because of the rain, a lot of people played two matches, including me," Muguruza said. "The second one was very tough, and I remember that as soon as I went after the match to my room, I started to have a pain in my left achilles. The next morning was even more painful.
"I have been carrying this since that day. And here, I have been training but on and off, honestly, because of the pain. 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."
Muguruza says after Doha felt pain in her left achilles. Hurts to serve and move side-to-side. Trainer says possible inflammation.
? WTA Insider (@WTA_insider) February 21, 2017
The reigning French Open champion began the season strong, following up a run to the semifinals of the Brisbane International with the quarterfinals of the Australian Open. She returned the the court for Fed Cup duty, going 1-1 in her singles matches, before losing to Zhang Shuai, 7-6(3), 3-6, 7-5, last week in Doha.
Her retirement in Dubai is her second injury retirement of the season, having succumbed to an abductor injury in Brisbane.
"Obviously I want to compete, so I'm going to go on the court trying to see if it goes better," Muguruza said. "Sometimes when you are out there and you get excited, you kind of forget sometimes. It's very hard, because in the past I went to the court and I [made the injury worse], and then I have to take two weeks to recover from that. I'd rather prevent that and maybe next week keep playing."
Muguruza's next scheduled tournament is the BNP Paribas Open in Indian Wells, California, which begins on March 6th.
"I'm quite disappointed, because they are very important tournaments, Doha and Dubai together, especially here this year," Muguruza said. "I feel kind of like I didn't play enough, you know? My next stop is Indian Wells, and I will try my best to be ready there."
? WTA (@WTA) February 21, 2017