PARIS, France - Former World No.1 and three-time champion Serena Williams was forced to withdraw from the French Open ahead of her fourth round match against Maria Sharapova due to an injury.
The highly-anticipated round of 16 match was set to be the fourth match on Court Philippe Chatrier on Monday, but Williams' injury gives Sharapova a walkover into the quarterfinals.
"I've unfortunately been having issues with my pec muscle and unfortunately it's been getting worse," Williams told reporters in a press conference.
"Right now, I can’t actually serve so it’s actually hard to play when I can’t physically serve.
"It didn't start before I got here. The first time I felt it was against Goerges in my last match. That's when I started to feel it. It was really painful and I didn't know what it was."
Williams' appearance at this French Open was her first at a Grand Slam since the birth of her daughter in September, and the former World No.1 scored victories over Kristyna Pliskova, No.17 seed Ashleigh Barty and No.11 seed Julia Goerges over week one in singles.
In addition, she and sister Venus accepted a wildcard into the doubles draw, where they were eliminated by No.3 seeds María José Martínez Sánchez and Andreja Klepac in three sets in the third round on Sunday.
"In my doubles yesterday, I tried a lot of different tapings and support to see how it would feel under match circumstances. I'm not serving that often; I'm serving once every four games...I thought it was a perfect opportunity to see how I was. It didn’t get a lot better."
Sharapova, winner of the title in Paris in 2012 and 2014, will face the winner of No.3 seed Garbiñe Muguruza and Ukrainian Lesia Tsurenko for a spot in the semifinals.
“It’s very difficult because I love playing Maria," the 23-time major champion added. "It’s a match I always get up for and her game matches up against mine.
"I made a promise to myself and to my coach and to my team that if I'm not at least 60% or 50%, then I probably shouldn't play. The fact that I physically can't serve at all is a good indication that maybe I should just go back to the drawing board and stay positive and try to get better and not get it to a point where it could be a lot worse."
The American also revealed that she will remain in Paris to undergo an MRI on Tuesday.
"I'm going to stay here and see some of the doctors here, see as many specialists as I can. I won't know [about Wimbledon] until I get those results," she said.
"I just always try to think positive and just think of the bigger picture and hopefully the next events and the rest of the year."
On the American's withdrawal, Sharapova said: "I was looking forward to my match against Serena today and am disappointed that she had to withdraw. I wish her a speedy recovery and hope she returns to the tour soon."