The World Anti-Doping Agency has yet to decide whether to appeal the decision to exonerate U.S. Open champion Jannik Sinner of blame for his positive steroid tests, and has another three weeks to do so.

WADA shared details of the appeal deadline with The Associated Press on Tuesday showing that the World Anti-Doping Code — the global set of rules for international sports — gives the Montreal-based agency at least until the end of September to file an appeal in the Sinner case.

WADA and Nado Italia, Italy's anti-doping agency, are the only two agencies that could challenge the decision by an independent tribunal announced by the International Tennis Integrity Agency (ITIA) on Aug. 20.

While the doping rules state that any other party with a right to appeal — such as Nado Italia — has 21 days to do so, WADA then gets another 21 days on top of that before its own window closes.

Tuesday marks the 21st day since the ruling by a three-judge panel in London was announced, but Nado Italia has yet to file an appeal.

WATCH l Sinner tops Fritz 6-3, 6-4, 7-5 in men's final at U.S. Open: 

Sinner beats Fritz to claim his 1st U.S. Open title

Italy's Jannik Sinner defeats Taylor Fritz of the United States 6-3, 6-4, 7-5 in the men's final at the U.S. Open.

However, it was unclear whether the initial 21-day deadline expired Tuesday, since that window opens only after all the parties receive the verdict and supporting documents, which can be at least a few days or more after the announcement, according to the tennis integrity agency.

"The deadline for filing an appeal to the CAS will be 21 days from the date of receipt of the reasoned decision in question by the appealing party," the tennis integrity agency rulebook says.

Then WADA has another 21 days to file an appeal to the Court of Arbitration for Sport in Lausanne, Switzerland.

Sinner tested positive twice for an anabolic steroid in March but ultimately was not banned because the ITIA determined he was not to blame. Sinner's accepted explanation was that the banned performance-enhancer entered his system unintentionally through a massage from his physiotherapist, who used a spray containing the steroid to treat their own cut finger.

The doping case was kept secret until last month's announcement and the top-ranked Sinner went on to beat Taylor Fritz in the U.S. Open final on Sunday.

An appeal could jeopardize his U.S. Open title but Sinner and his legal team have provided detailed evidence that persuaded the ITIA and the tribunal judges that his explanation was credible.