Serena Williams pulled out of the French Open shortly before her scheduled fourth-round match against Maria Sharapova, saying she had suffered a pectoral injury that prevented her from being able to serve.

Williams was playing in her first Grand Slam singles tournament since winning the Australian Open in January 2017. She’s played only intermittently this season after giving birth to her first child in September, and her appearance at the French Open, which she has won three times, appeared to mark her real return to the sport. She will have an MRI on the injury, she said, and remains hopeful about playing in Wimbledon in early July.