The International Equestrian Federation (FEI) has been forced to re-open the bidding process for the 2022 World Equestrian Games after sole candidate Šamorín withdrew from the contest.
The Slovakian city had been due to stage the event after American city Lexington pulled out of the race in January.
But Šamorín refused to sign the host city contract despite "lengthy discussions" with the FEI.
A host city for the event will be announced at the FEI Bureau meeting in Manama in November of next year.
Šamorín's decision to withdraw was announced by FEI President Ingmar de Vos at the governing body's General Assembly in Montevideo.
Their withdrawal marks the latest difficulty for the FEI and the World Equestrian Games but De Vos, who became a member of the International Olympic Committee (IOC) in September, claims he is confident a suitable host will be found.
"We are confident there will be candidates, but these are complex Games and we need to make sure we do it right," he said.
Šamorín hosted last year's FEI World Endurance Championships after stepping in to replace Dubai.
The United Arab Emirates city was axed due to horse welfare concerns.
The 2018 World Equestrian Games are due to held at the Tryon International Equestrian Center in North Carolina in the United States between September 10 and 23.
The city replaced Bromont in Canada, which had been selected to host but was then hit by financial issues.
Šamorín pulling out was among a number of key decisions announced at the General Assembly in the Uruguayan capital.
The FEI's membership approved the qualification process for the sport's three Olympic disciplines: jumping, dressage and eventing - at Tokyo 2020.
An initial deadline achieve minimum eligibility requirements to compete at the Games was due to be May 18 in 2020 but that has been altered to five weeks before the sports entry deadline, due to be confirmed by the IOC next year.
Plans to introduce a new scoring system for international dressage tests were also scrapped by the FEI following a mixed response from the organisation's members.
It would have seen the implementation of a "hi-lo" drop score, which removes the highest and lowest scores for each movement so an average mark is formed.
De Vos claimed during his opening address that the sport was "expanding at an amazing rate" and was continuing to grow and develop.
"In 10 years the number of events have more than doubled and we are now seeing a steady and annual increase of around eight per cent in terms of events and four to five per cent in terms of registered athletes," he said.
"These are incredible statistics - especially in this very diverse and competitive sports market.
"And not only is our sport growing but the quality and the presentation is better than ever."
insidethegames has contacted the FEI for further clarification on the bidding process for the 2022 World Equestrian Games.