The Diving World Cup in Tokyo has reportedly been cancelled by the sport's international governing body Fina because they believe the organisers' planned Covid-19 precautions will not ensure athletes' safety.
"Fina sincerely regrets this situation," read the letter seen by BBC Sport.
"Despite all best efforts and understanding from Fina, the executive was obliged to take this drastic decision.
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"In their view, this plan will not properly ensure health and protection guarantees to participants."
It is also understood Fina are unhappy about numerous Japanese embassies yet to issue visas for athletes due to compete, rising costs associated with implementing Covid-19 measures and the insistence of a three-day quarantine.
The World Cup event was due to take place from April 18-23.
It was meant to serve as an official test event for Tokyo 2020 and was slated as the final qualifier for the Games this summer. Fina is now reportedly trying to find another venue.
"We have received an email from Fina last night," said Tokyo 2020 president Seiko Hashimoto.
"What kind of measures would make this test event possible and the allocation of dates?
"I believe there are still many variants which need to be discussed and we haven't been filled in with all the details yet so we would like to continue listening to them [Fina]."
Great Britain had named a strong team for the event, with two-time Olympic medallist Tom Daley and Rio 2016 champion Jack Laugher among those set to compete.
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