World number two Simona Halep has withdrawn from the Stuttgart Open with a hip injury.
The 27-year-old sustained the injury during her win over Caroline Garcia in Romania's Fed Cup defeat by France on Sunday.
But Halep is hopeful she will be fit for next month's tournaments in Madrid and Rome before defending her French Open title from 26 May.
"If I'm not 100%, I don't want to step on the court," Halep said.
"I'm also exhausted mentally because I gave my everything in that tie but unfortunately we couldn't win.
"That's why I decided to pull out, because I have to think about my health first.
"I've been very sad the last two days. I've been through these moments many times, so I know how to handle it. I just need to recover mentally and physically and then just start again."
Spain's world number 19 Garbine Muguruza also had to pull out of Stuttgart through illness.
Dutch sixth seed and world number seven Kiki Bertens progressed to the second round in straight sets as she defeated Germany's Anna-Lena Friedsam 7-5 6-2 on Tuesday.
Seventh seed Anastasija Sevastova advanced with a 6-2 4-6 6-0 victory over fellow Latvian Jelena Ostapenko and Russia's Daria Kasatkina edged Belgian Elise Mertens 7-6 7-5.
Meanwhile, Andrea Petkovic set up an all-German second-round tie against world number five Angelique Kerber with a 6-3 6-4 win against Sara Sorribes Tormo.