Since the creation of the WTA Tour - which is celebrating its 50th anniversary - only two world number ones have never lifted a Grand Slam trophy: Jelena Jankovic and Dinara Safina. Before long, that unenviable club could be joined by a third member in the shape of Karolina Pliskova.
Pliskova topped the rankings for eight weeks in 2017 - not the longest reign in history, that goes without saying. However, after many years of circling the globe, it seems that she is no longer in a position to fight for a Grand Slam title, having been overtaken by a new generation and struggling to rediscover her best game.
During her heyday, it was hard to compete with the Czech, who had perhaps the best serve of the 2010s. She was voted 'Ace Queen' in 2015, 2016, 2017, 2019 and 2021, with a peak of 530 aces in 2016 - just mind-blowing. It was a weapon of mass destruction.
But it's not enough to have a serve, you have to do something with it when the ball comes back. And in her best years, she had the ability to close out points in two strokes, three at most. Of course, taking risks led to errors, but as long as the number of winning shots remained higher, everything was fine.
This was particularly the case at her two biggest WTA 1000 titles, and especially at Cincinnati in 2016, when she annihilated Angelique Kerber, leaving the German with just four games to her name. However, in the rematch three weeks later in the US Open final, Kerber learned from her mistakes, made her rival play to the maximum and caused her to commit no fewer than 47 unforced errors. Her first shot at a Grand Slam had vanished.
The second was at Wimbledon in 2021. A splendid tournament, undoubtedly the finest of her career, particularly in the semi-finals where she ousted Aryna Sabalenka after a great match. But to her misfortune, she came up against the best returner on the circuit, Ashleigh Barty, in the final, and despite putting up a huge fight, gave up eventually. However, she was still in her prime, and the jackpot would eventually arrive, we all thought.
But it seems that something broke along with her hand at the beginning of 2022. Since then, we've never seen the same woman, the one who inspired fear in her rivals. The player who was almost always the favourite in those matches, a top-five player in the world.
In the last two years, with the retirements of Ashleigh Barty and Serena Williams, the WTA Tour has become increasingly crowded. Iga Swiatek seemed out of reach but almost lost her world number one ranking at Roland Garros - and that could still happen at Wimbledon. There are more than twenty contenders on the circuit with the level to match her.
Of course, Pliskova is one of them but there are signs that she's on a slippery slope. The Czech had to endure the affront of qualifying for the main draw in Adelaide and Doha earlier this year. She succeeded, but that's not the point.
More importantly, another streak came to an end - that of six years without defeat in the first round of a Grand Slam tournament. At the last French Open, she fell at the first hurdle to Sloane Stephens.
'It wasn't her best surface,' she was quoted as saying at the time. That's not necessarily untrue but it's a surface on which she has reached the final of the WTA 1000 in Rome three years in a row, winning her second and last title there in 2019.
Indeed, her win/loss record of 19/12 in 2023 is quite respectable but apart from a quarter-final loss to Magda Linette at the Australian Open, there hasn't been much to show for it. We expected to see her shine on grass again this season but in three matches she has only beaten Elise Mertens via retirement and lost to Petra Kvitova and Daria Kasatkina - not just anyone but the kind of rivals she might find on the road to a Grand Slam title.
The clock is ticking for Pliskova, who is in real danger of joining the unfortunate aforementioned club. Not that that would be a disgrace since she will have had a fine career whatever happens. However, compared to Jankovic and Safina, her talent was, and still is today, infinitely superior. In this respect, she could become the greatest player in history never to have won a Grand Slam.