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Serena Williams has pulled out of the French Open tennis at Roland Garros.
She pulled out before her 4th round clash against Maria Sharapova because of an injury that affected her serve.
The 23-time Grand Slam winner recently returned to tennis after giving birth to her first child, but looked in good form in her opening matches.
"I've had issues with the right pectoral muscle to the point where I can't serve," said the 36-year-old.
"I'll have a scan. I won't know about Wimbledon until I get the results."
Williams said she first felt the problem during her third-round win over German 11th seed Julia Gorges on Saturday.
31-year-old Sharapova of Russia, a two-time winner at Roland Garros, will now play either Spain's 2016 champion Garbine Muguruza or Ukraine's Lesia Tsurenko in the last eight.
The meeting of the two former champions, both making comebacks at Roland Garros this year, was set up when Williams beat Gorges shortly after Sharapova beat Czech sixth seed Karolina Pliskova.
The pair have had a frosty relationship since they first met on court in 2003, although Williams said in her pre-match news conference on Saturday that she did not have any "negative feelings" towards the Russian.
There has not been much of a rivalry on court in recent years, Williams having won 19 of their 21 meetings. Both of Sharapova's wins came in 2004 - including that year's Wimbledon final.
Tuesday's MRI scan will reveal more, but if there is no serious damage, then Wimbledon may still be very much within Williams' sights. There are still four weeks to go, and not being able to play a grass-court warm-up event beforehand should not be a concern: only twice in her career has she done so.
