"This year again, tournament officials will establish the list and ranking of the women's seeds based on the WTA ranking," the French Tennis Federation said, per the Associated Press (via ESPN.com). "Consequently, [the seeds] will reflect this week's world ranking."
Williams has competed in just two WTA events this year after returning to the court following the birth of her daughter. Because of that, as well as her absence for almost the entire 2017 campaign, she sits No. 453 in the WTA rankings.
Both Maria Sharapova and Simona Halep lobbied on Williams' behalf for her to earn a seed at the 2018 French Open.
Sharapova said returning from pregnancy requires "an incredible effort" that can tax a player physically and emotionally, while Halep said it's "normal to give birth" and "good to protect the ranking when someone is giving birth."
Williams won the 2015 French Open and was the runner-up in 2016. Failing to be seeded this season will leave her hopes of a fourth French Open title in serious jeopardy.
Williams received a wild card entry for her return at the BNP Paribas Open in Indian Wells, California, in March. As a result, she played No. 29 Kiki Bertans in the second round and sister Venus, who was seeded eighth, in the third round. Serena lost to Venus in straight sets. In her next event, the Miami Open, a meeting with fourth-seeded Elina Svitolina awaited Williams if she had defeated Naomi Osaka in the first round.
Something similar could happen again at the French Open without the luxury of a seeding designation.