Sinner's US Open Defense Is Over: Polymarket Moves from 32¢ to 0¢ in 48 Hours

The defending US Open champion will not be in Flushing Meadows. Jannik Sinner's formal withdrawal on August 21 rendered the market's most straightforward question in tennis — can the World No. 1 repeat? — equally straightforward to answer: no.

TL;DR

Jannik Sinner officially withdrew from the 2026 US Open on August 21, citing an unresolved right knee injury that has kept him off the competitive court since winning Wimbledon in July.
Polymarket priced him at 32¢ as recently as August 20; by the morning of August 22, that figure had collapsed to 0¢ — a -32¢ move in under 48 hours.
The withdrawal follows a cascade of negative signals across six weeks: missed Montreal, missed Cincinnati, shockwave therapy, multiple medical assessments, and a training return to Monte Carlo that confirmed he still is not ready.
Carlos Alcaraz, fresh off his own comeback announcement, now sits at 34¢ as the market's top remaining contender in a field that no longer includes the defending champion.

What the Market Says

At press time (2026-08-22 10:43 UTC), Polymarket's market on whether Sinner wins the 2026 Men's US Open reads YES at 0¢ and NO at 100¢, with 24-hour volume of $145,938. That volume figure is notable — nearly $146,000 traded in a single day on what is now, mathematically, a settled question.

The price path tells the real story. On August 16, Sinner was trading at 50¢ — even odds for the reigning champion and World No. 1. That is a number most analysts would have considered reasonable for a healthy Sinner at the start of a Slam. But the injury signals were already accumulating, and the market read them. By August 19 that had compressed to 28¢. A brief technical rebound on August 20 pushed the number back to 32¢ — perhaps traders pricing in the faint possibility of a last-minute fitness declaration. The formal withdrawal on August 21 removed that optionality entirely, and by the morning of August 22 the market had zeroed him out.

Thirty-two cents erased in 48 hours. The arithmetic is blunt.

The Case

The withdrawal was confirmed by multiple outlets including ESPN, ABC News, and BBC Sport across August 21 and 22. The underlying cause is a right knee injury that predates Wimbledon — meaning Sinner carried it through what became a Grand Slam victory — and has proven resistant to treatment in the weeks since.

The treatment timeline is worth laying out clearly. Sinner underwent shockwave therapy in mid-August. He had multiple medical assessments in early August. He withdrew from both the Montreal and Cincinnati Masters 1000 events, forfeiting ranking points and match sharpness in the process. Then, according to his statement reported by MARCA on August 21, he returned to the court in Monte Carlo in the 48 hours before announcing the withdrawal — and found that the knee still was not ready.

His own words are direct: "we have returned to the court in Monte Carlo over the last few days and realized that I still need more time to recover from my right knee problem." And separately: "Even though I have been working hard with my team and medical staff, we have now had to make the difficult decision that I will not be able to compete in this year's US Open."

The personal dimension is worth acknowledging. Sinner also noted that New York holds a special place for him and that he was genuinely looking forward to returning to the crowd at Arthur Ashe. A player does not walk away from a title defense because the medical staff thought he might feel a little sore. Six weeks without competitive play, two Masters withdrawals, and shockwave therapy are not indicators of a minor niggle.

The timing adds an ironic dimension. This withdrawal lands approximately 24 hours after Carlos Alcaraz — Sinner's chief rival and a player he has been measured against for the last two years — announced his own return to the same tournament after a four-month wrist injury absence. Alcaraz is now the market's leading active contender at 34¢ (as of the same press-time capture), stepping into a vacuum created directly by Sinner's exit. The two men have spent the last 18 months trading Grand Slam titles and the No. 1 ranking back and forth. For the 2026 US Open, one of them gets to show up. The market has priced that asymmetry accordingly.

For traders who held YES positions on Sinner going into this week, the exit price was 0¢. There is no softer way to state that.

Risks

The 0¢ price leaves exactly zero room for further downside — which is, technically, the honest definition of maximum certainty. But a few observations for the skeptical reader.

First, the withdrawal is formal and unambiguous. This is not a will-he-won't-he situation subject to last-minute reversal. The US Open qualifying and draw processes have deadlines, and Sinner's team has made the decision public. The probability of this market resolving YES is, at this point, a rounding error on a rounding error.

Second, some portion of the $145,938 in 24-hour volume may represent traders closing hedged positions or exiting residual YES exposure at 0¢ rather than holding to resolution. The headline withdrawal captures a process of escalating injury signals that began in early August — meaning some informed participants likely trimmed or closed their longs well before the formal announcement. The market, in other words, did not miss this entirely; it discounted it progressively from 50¢ over six days. The final leg from 32¢ to 0¢ is the confirmation trade, not the discovery trade.

Third, market resolution is September 13, 2026. Between now and then, nothing changes the fundamental fact of the withdrawal. The NO position at 100¢ offers no yield and no further upside — it is simply waiting for a calendar to advance. The interesting question is not this market; it is what Sinner's injury timeline implies for the rest of the 2026 season, and whether he returns healthy for the indoor hard-court swing in the fall. That is a separate market question, and one worth watching.

For now, the defending champion is watching from Monte Carlo, and the 2026 US Open will have a new men's singles winner by September 13. The market is certain. The rest of the draw is not.

Prices captured at press time and are not live. Not financial advice. Independent publication - not affiliated with Polymarket, Banana Gun, or any venue.