Former world number one Serena Williams will not be seeded at this year's French Open, according to the organisers of the May 27-June 10 claycourt Grand Slam.

Williams, a three-time champion at Roland Garros, discovered she was pregnant after winning 2017 Australian Open and following her return from maternity leave in March, the American suffered early defeats in Indian Wells and Miami.

The 36-year-old subsequently withdrew from Madrid and Rome claycourt events and the 23-times Grand Slam champion has seen her world ranking tumble to number 453.

"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 told The Associated Press.

"Consequently, (the seeds) will reflect this week's world ranking," the organisers added.

Williams, who gave birth to daughter Alexis last September, can compete at Roland Garros under the WTA's special ranking rule, which allows players returning from long spells out to use their ranking at the start of their absence.