A few weeks ago, Elena Rybakina looked like she might not even make it to the US Open after a worrying leg injury forced her to retire against Iga Swiatek in Cincinnati. Instead, the Kazakh has shown up in New York looking like nothing ever happened, putting together one of her cleanest runs at Flushing Meadows and reaching the fourth round without much trouble. But now comes Naomi Osaka, and this is where things could get uncomfortable.

Andy Roddick believes Rybakina still has not faced anyone capable of truly testing that injured leg, and Osaka’s brutal baseline power could be the first real test of whether she is actually healthy or has simply been getting away with it. “Rybakina has been healthier than we thought,” he said on Served with Andy Roddick. “The one thing that I’m curious about is that she hasn’t had to react quickly to the weight of shots of someone like Osaka.”

That is where Roddick sees the danger. Rybakina has looked comfortable when she has time to move rhythmically into the ball, but Osaka can take that time away in a hurry. “Osaka can knock her off her mark and make her move quickly,” he added. “If this is an injury where you can’t brake quickly, you can’t use that quick twitch… I don’t know that we’ve seen it to the level that Osaka will make her move. That is something to watch for.”

And Roddick has a point. Osaka has already hit a 122 mph serve at this US Open, faster than Rybakina’s 120 mph best, and that kind of pace can rush the Kazakh before she gets properly set. That matters after her recent leg trouble, because Osaka can force the sudden lateral movements and quick changes of direction that Rybakina has not consistently faced so far.

The twist is that Osaka is not fully healthy either, having admitted she has been dealing with an Achilles issue since the grass season.

Rybakina has beaten Thea Frodin, Jessica Bouzas Maneiro, and Yulia Starodubtseva to reach the fourth round, but the road has not exactly been brutal. Frodin lacked Grand Slam experience, while Bouzas Maneiro is far more comfortable on natural surfaces.

Starodubtseva was a tougher test, with a strong baseline game built for long rallies. But Osaka is a different beast altogether. As Roddick pointed out, her power can rush Rybakina in ways nobody has so far, and this is a two-time US Open champion who has played some of her best tennis in New York.

Rybakina and Osaka have met just once, with the Kazakh winning their recent Canadian Open clash. But Osaka had the match in her hands after taking the first set and leading 4-2 in the second. She failed to close it out, and Rybakina made her pay, taking control with her groundstrokes before dominating the third set on serve with eight aces and just three first-serve points lost.

To beat Osaka again, Rybakina will need that same level and, more importantly, a healthy body. But their US Open runs could hardly look more different, and their reactions after the third round said plenty about where both players are right now.

Elena Rybakina and Naomi Osaka Have Had Opposite Campaigns at the US Open

While Rybakina’s US Open campaign has been a confident one, with the World No.2 yet to drop a set in New York this year, Osaka’s performances have not been at her best, with the Japanese player’s serve being an issue as well as the large number of unforced errors coming from her racket.

The on-court interviews were a great representation of both players’ mindsets. After her third-round win, Rybakina cheekily corrected her interviewer about her US Open record, whereas Osaka apologized for her on-court behavior against Elise Mertens, saying she was surprised she had managed to win the match.

The serve will be a big point in the match, as Rybakina’s serve is one of the best in the WTA, and the Kazakh does have the ability to hit aces at will. On the other hand, Osaka has been broken 10 times in 3 matches and has often struggled despite leading. Moreover, the match has an added dimension with Rybakina in contention for the No. 1 ranking, which she will achieve should she reach the semifinals.