Wimbledon champion Simona Halep has a "small tear" in her calf after being injured in the Italian Open.
The injury casts doubt on the 29-year-old's hopes of playing the French Open - which she won in 2018 - that starts this year on 30 May.
Wimbledon, which was cancelled last year, starts on 28 June.
"After an MRI here in Rome I can confirm that I have small tear high up in the left calf," said Halep.
"I will fly home and begin recovery in the pool and gym on Monday. I'm staying positive and will do everything I can to speed up my return."
Halep, who was defending her title in Rome, was leading 6-1 3-3 in the second-round match against Kerber when she was forced to quit.
Australian world number one Ashleigh Barty is among those hoping to succeed her as champion and faces American teenager Coco Gauff in the quarter-finals on Friday.