Williams is currently dealing with a severe case of the flu and looked extremely unwell during her 4-6, 6-3, 6-0 semi-final victory over Timea Bacsinszky on Thursday.
During that match, Williams constantly smothered herself with cold towels and cut her on-court interview short following a coughing fit. She even skipped her post-match press conference to speak with the tournament doctor.
While there has been no word about Williams not playing in the final, she did not practise or show up for her press conference on Friday.
"I started to feel unwell around the third or fourth round and I felt really terrible during the semis against Timea," Williams said via a statement. "I’m actually not sure how I got through the match and when it was over I just kind of collapsed. I couldn’t move.
"I saw the tournament doctor on site and since I came home I’ve been resting – I just could not practice today. I think I have some kind of flu which makes it tough, because it’s just a matter of resting and keeping hydrated – there’s not much else I can do."
Besides the flu, Williams has endured a tough French Open campaign as her bid to win her third Roland Garros title has seen her register come-from-behind wins in four matches, which is a career-best for her in a Grand Slam.
"I need time and obviously don’t have a lot of it but it helps that I can be at my apartment and have my family and friends with me," she said. "Being in the final here in Paris means so much to me and it’s very upsetting that I feel so lousy right now.
"It’s really unfortunate to be like this at the grand slam where I feel so at home and really want to win. I just have to hope that tomorrow I will be feeling a lot better and able to give my best on the court."