Despite her first loss to Muguruza in their fourth meeting, committing 27 unforced errors and getting broken six times, Sharapova said she saw signs of hope in her form as she builds towards Wimbledon next month.
The 36-year-old said she had suffered a pectoral muscle injury in her third-round win over Julia Goerges and "can't serve at all".
Serena Williams said she had suffered a pectoral muscle injury in her third-round win over Julia Goerges and "can't serve at all".
Maria Sharapova's last win over Serena Williams came at the 2004 WTA Tour Championships -- before even the birth of Twitter and YouTube.
Sharapova and Serena have met 21 times, with the American leading the head-to-head record 19-2 after 18 consecutive wins dating back to 2004.
Former champion Garbine Muguruza reached the French Open last 16 with a comfortable 6-0, 6-2 win over Australia's Sam Stosur
Serena Williams, seeking a 24th Grand Slam title, will face Germany's Julia Goerges for a place in the French Open last 16.
Highly-rated Canadian teenager Denis Shapovalov was knocked out by Germany's Maximilian Marterer 5-7, 7-6 (7/4), 7-5, 6-4.
Three-time champion Serena Williams will make her eagerly-awaited return to Grand Slam tennis on Tuesday with a French Open first-round match against Kristyna Pliskova on Court Philippe Chatrier.
Roland Garros organisers have come under fire for not seeding 23-time major champion Williams for the French Open.
Serena Williams' preparations for Roland Garros have prompted a debate over whether she should have been given a special dispensation and been seeded for the tournament.
Serena and Venus Williams have won 14 Grand Slam doubles titles as a team.
Former world number one Williams, now ranked a lowly 453, is playing a Grand Slam for the first time since she won her 23rd major at the 2017 Australian Open after which she stepped off the tour to give birth to her daughter in September.
The decision by French Open organisers not to grant Serena Williams a seeding on her long-awaited Grand Slam return has prompted renewed focus on the sport's policy towards female players and parenthood.
Serena Williams has pulled out of the Madrid WTA tournament due to a high fever, organisers said Thursday.
Serena Williams is currently 449th in the WTA rankings after taking time off to get married and have her first child last year.
Serena Williams crashed out of the Miami Open in the first round here Wednesday, slumping to a straight sets defeat against Japan's Naomi Osaka in the latest setback to the former world number one's comeback.
Caroline Wozniacki says it would be "impossible" for her to follow Serena Williams' lead and return to tennis after giving birth.