"I unfortunately have been having some issue with my pec [pectoral] muscle," she told reporters in an impromptu press conference. "Right now I can’t actually serve, so it’s hard to play. I can’t physically serve.
"It's very difficult because I love playing Maria. Her game matches so well against mine."
Williams said the new injury first surfaced during her third-round victory over Julia Goerges, and efforts to strap her shoulder to protect the muscle made little impact during her doubles defeat alongside sister Venus Williams on Sunday.
"It didn’t start before I got here," Williams said. "It was really painful and I didn’t know what it was. I’m going to get an MRI tomorrow, I’ll stay here and see some doctors here, but I won’t know about [Wimbledon] before that.
"I'm beyond disappointed. I gave up so much – time with my daughter time with my family I put everything on the court all for this moment. So it’s really difficult to be in the situation. [But] I try to think positive and think of the bigger picture, the next events and the rest of the year."