PARIS -  Serena Williams' bombshell pregnancy announcement last month triggered a sequence of events that has left this year's women's draw at Roland Garros wide open and primed for a new champion.

The 23-time Grand Slam winner learned she was pregnant just two days before starting a successful assault on January's Australian Open and won't return before next year.

The French federation then refused to award Maria Sharapova a wild card for the tournament with the Russian on the comeback trail following a 15-month doping suspension. With Li Na long since retired that means the winners of five of the past six French Opens -- Williams (2013, 2015), Sharapova (2012, 2014)nd Li (2011) -- are absent from the field, while several pretenders to the Coupe Suzanne Lenglen are battling injury and loss of form.

Simona Halep, the 2014 runner-up, established herself as arguably the leading challenger by winning the Madrid Open before reaching the Rome final, but an ankle injury has hampered her preparations.

The Romanian, who faces Slovakia's Jana Cepelova in the first round, earlier this week rated her chances of playing in Paris as just "50-50". But after practice on Friday, Halep sounded far more confident. "I expect to play, I should be OK but I am waiting for another ultra-sound on Saturday," said Halep, who arrived early in Paris for treatment on torn ligaments.

World number one Angelique Kerber has endured a miserable clay-court season, losing early in Stuttgart and crashing out in her Rome opener, while retiring from her last-16 clash in Madrid with a lower back injury.

The German opens with a tricky first-round tie against fellow left-hander and former top-10 player Ekaterina Makarova. Defending champion Garbine Muguruza's fortunes on the surface have proved almost as bleak.

Her only three wins came in Rome where she reached the semi-finals before a neck injury forced her to quit against eventual champion Elina Svitolina, the fourth time the Spaniard has failed to complete a match in 2017.

Muguruza begins her title defence against 2010 champion Francesca Schiavone, the wily veteran making her final French Open appearance before retiring at the end of the year.