Predicting anything in tennis is a dangerous game. Throughout its long history, the sport has delivered every conceivable narrative arc. Early breakouts followed by fizzling out? Check. Slow starts transformed into late-bloomer glory? That too. If it could happen, it probably already has, so nothing should really surprise us anymore.

That said, some troubling trends suggest that 2026 will be a defining year for certain players. It doesn’t mean their careers are doomed if things don’t go well, but we’re talking about the present moment and what needs to happen now. Here are five players who have everything to prove this season.

Taylor Fritz

Taylor Fritz is a veteran at this point. At 28, he’s neither a next-gen prospect nor an emerging talent. He’s smack in the middle of his prime. What he accomplishes now will likely define the peak of his career. So why is 2026 so crucial?

Because he’s at a crossroads. Either he takes the next step and becomes a legitimate contender, or he continues hovering just below that elite tier, occasionally winning titles but never seriously threatening at the biggest events.

On paper, his 2025 season looked solid: 55 wins, 25 losses. The problem? It was essentially the same as 2024. No real progression, and in some ways, a step backward. In 2024, Fritz reached five finals, including the US Open and ATP Finals, winning two titles. In 2025, he made just three finals and won two. That’s not an improvement. If anything, that’s stagnation.

More talented players are rising through the ranks, and if Fritz doesn’t elevate his game now, he risks becoming another Tomas Berdych: very good, but never quite good enough to challenge the elite. There’s certainly another level he can reach. Maybe he won’t become a Grand Slam contender, but he could absolutely become a regular Masters 1000 threat, something he hasn’t achieved yet.

The direction of his career will be determined in 2026. It’s now or never.

Daniil Medvedev

In many ways, Medvedev has already accomplished more than enough. He’s won a Grand Slam, had legitimate shots at several others, reached world No. 1, and dominated the sport for stretches. He won’t be remembered as one of the all-time greats, but he’ll certainly be remembered as a great player who, at his peak, was a force.

So what does he have to prove? Simple: whether he’s still relevant.

We’ve seen the dominant version of Medvedev, and at his best, he’s still capable of that level. But we haven’t seen it consistently in a while. Let’s look at the numbers. In 2023, he won 66 matches, the most in his career. In 2024, that dropped to 46, a year many considered disappointing. In 2025, he won even fewer (42), making it his least impressive season in years.

He’s been noticeably more irritable and frustrated lately, which suggests something is bothering him. And why wouldn’t it? He’s only 29, nowhere near retirement, yet the decline is undeniable.

That makes 2026 a test. Will he continue sliding into irrelevance, or will he recapture some of that former glory? Currently sitting at No. 13, he’s already in danger of losing key seeding positions, which means tougher draws, which could lead to earlier losses. It’s a snowball effect, and it’s picking up speed.

Andrey Rublev

Another Russian once touted as a future Grand Slam champion is Andrey Rublev. Unlike Medvedev, though, Rublev never hit those same peaks. He’s won plenty of titles, made a fortune, beat top players, and might end up in the Hall of Fame. But the big ones? Especially Grand Slams? That’s where the story gets bleak.

It’s been eight years since Rublev made his first Grand Slam quarterfinal at the 2017 US Open. Since then, he’s added nine more quarterfinal appearances. But here’s the kicker: not a single semifinal. He’s 0-10 in Grand Slam quarterfinals. For a 28-year-old who isn’t getting any younger, that’s a damning statistic.

What’s gone wrong? It’s hard to say. He’s beaten top players before, but something doesn’t click at the majors. Whether it’s pressure or mental fragility, he hasn’t cracked the code. And 2026 is pivotal, especially considering he failed to reach a single Grand Slam quarterfinal in 2025, dropping him out of the Top 10 and dangerously close to falling out of the Top 20 entirely.

This season is massive for Rublev. Winning a Grand Slam feels like a distant dream at this point, but will he even return to being a consistent Top 10 player? The talent is there, but talent alone won’t cut it.

The big question is whether Marat Safin, now working with Rublev, can mold that raw ability into something less self-destructive and more focused. Safin managed it for himself, albeit briefly. If Rublev could capture even one of those magical Safin years, it would completely redefine his legacy.

Alexander Zverev

The poster child for “not having done enough” is, without question, Alexander Zverev. He was billed not just as a future Grand Slam winner, but as a multiple-time champion. That hasn’t happened. He still hasn’t won a major, and with each passing year, more people question whether he ever will.

He remains a fantastic player. Even after his devastating ankle injury, he’s proven himself to be the third or fourth best player in the modern game. But the big one keeps eluding him. Every time he has a real chance, he falls short, proving he’s just not quite at the level required.

With Sinner and Alcaraz continuing to improve and younger players emerging, Zverev’s window is shrinking fast. Still, 2026 offers four fresh opportunities at the majors, assuming he stays healthy. That alone makes it a make-or-break year.

At this stage of his career, there are only two things missing from his resume: a Grand Slam title and the world No. 1 ranking. Those two accomplishments could go hand in hand if he finally breaks through. Keep a close eye on Zverev this year. The spotlight will be on him constantly, and the pressure will be immense.

Stefanos Tsitsipas

You can’t make this kind of list without mentioning Stefanos Tsitsipas. The Greek star is 27 now, entering what might be the final stretch of his athletic prime. And yet, he’s nowhere near where he once was. Currently ranked No. 36 after a dismal season, the fall has been steep.

He’s been playing lackluster tennis for a while now, and the decline has shocked some but not others. It’s not all about what happens on court, either. There’s been plenty of off-court drama that’s affected his focus. He remains a polarizing figure whose potential never fully materialized, which is genuinely disappointing. He had Grand Slam-winning talent in his hands, but he never got it done.

Still, 2026 offers a shot at redemption. You’d expect a strong push from him. Whether he can return to something resembling his glory days remains uncertain, but it’s hard to imagine him repeating the disaster that was 2025.

If he does? Then 2026 will be remembered as the year Tsitsipas faded into irrelevance. Let’s hope it doesn’t come to that. Either way, it’s time for Stefanos. Make or break.

Main Photo Credit: Susan Mullane-USA TODAY Sports