At the Italian Open in Rome, Osaka pulled out of her last eight clash with Kiki Bertens with an injury to her right thumb.
In Madrid at the same stage, she was downed by the Swiss player Belinda Bencic and she lost in the semi-finals in Stuttgart to Anett Kontavet. Osaka has not added any baubles to her trophy cabinet since the Australian Open in January.
Simona Halep, who won the French Open last year, is similarly without trophies this season.
She has had a couple of chances to wrest top spot in the world rankings from the Japanese 21-year-old before the French Open, but she fluffed her lines.
Her latest debacle came in the second round in Rome where she fell to the world number 44 Marketa Vondrousova from the Czech Republic.
"Mentally, I am pretty relaxed," Halep said on the eve of the French Open. "I know it's a little bit of pressure there, because I'm a defending champion. But it's first time that’s happened to me.
"Because I have the title already, it doesn't matter anymore what happens. Everything comes now comes as a bonus.
"I wanted the title badly. I wanted it so much that now having it, I just want to be happy and to smile."
Halep opens her defence against Australia's Ajla Tomljanovic. Halep won their only encounter in three sets on a hard court in Cincinnati last summer.
"It's going to be different because it's a clay court," Halep added. "But still it's going to be a very tough match. She's powerful. She hits the ball strong.”
Osaka and Halep will be seeded one and two respectively. And it will be a battle royal should they meet on the final Saturday of the 2019 extravaganza.
Who could possibly stop that slug fest in the showdown? Well, actually, quite a few people.
“You wonder who’s going to dominate the game on clay,” said French Open tournament director Guy Forget. “I think there are about 15 women who can say with some legitimacy: ‘It’s my year. I can win this'.
“The uncertainty is great,” Forget added. “It’s like when you go to see a movie and you’re on the edge of your seat right up until the last minute.”
The same old, same old haunts the men’s game with Rafael Nadal tilting for a 12th title. World number one Novak Djokovic bristles motivation to repeat his feats of 2016 and hold all four grand slams at the same time.
Admittedly it’s not all four in a calendar year. That hasn’t been achieved in the men’s game since Rod Laver in 1969.
Steffi Graf pulled off the coup in 1988 on the women’s circuit and the only player to approach that feat has been Serena Williams.
Her French open triumph in 2003 allowed her to achieve what she poetically dubbed the "Serena Slam"
Such sassy sibilance. And she repeated the sweep of four between 2014 and 2015. Williams will need all her panache to make inroads in 2019 in Paris.
She is the 10th seed but will lack match sharpness, especially after pulling out of the Italian open to nurse the left knee injury that has marred her season.
Though still a formidable presence, at 37, it is difficult to picture her celebrating her fourth Roland Garros crown and a 24th Grand Slam title.
In victory or defeat, Serena Williams is terrific theatre. But the 2019 French Open may be, even for her, a stage too far.