The Seattle Sounders won the Concacaf Champions League on Wednesday night, beating Pumas of Mexico, 3-0, to claim a 5-2 victory on aggregate in the two-legged final. The victory made Seattle the first team from Major League Soccer to lift the trophy in a generation, and gave the United States the continental title it has coveted for more than 20 years.

It should also make Seattle the first M.L.S. team to play in the FIFA Club World Cup.

Except that no one, not even FIFA, is sure when that event will take place, or what it will look like. The tournament’s traditional December window is unavailable this year because of the World Cup in Qatar, and grand plans for an expanded Club World Cup in China have gone nowhere after they were announced and then promptly disrupted by the coronavirus pandemic.

“No clue,” one FIFA official said in a text message when asked when Seattle could expect to take part in the event.

The Club World Cup has been held annually since 2005, with representatives of each of FIFA’s global confederations facing off to determine a world club champion. Top European teams have dominated the event, with the likes of Barcelona, Real Madrid, Bayern Munich, Liverpool and Chelsea lifting the trophy in the last decade. Facing off against teams like that in an international competition has been a dream for many M.L.S. players, executives and fans.

FIFA, which runs the Club World Cup, has been eager to expand the tournament, and it put a plan on the table for a 24-team tournament shifted to the summer and held every four years instead of annually. In a meeting in Shanghai in October 2019, it approved the change and awarded China the hosting rights for the first edition in 2021. The coronavirus soon made that plan unworkable.

The pandemic-delayed 2021 Club World Cup that was held in February, and won by Chelsea, was nominally the final one under the old, smaller format. Holding another one in 2022 could be problematic, with league schedules already being squeezed by the enforced break caused by the World Cup that opens in November. There has been talk of holding the first expanded version in the summer of 2023, but as of now there is no official date for the event.

Under the original plans for the expanded tournament, three teams from the Concacaf region — covering North and Central America and the Caribbean — would participate. One of them presumably could be the Sounders after Wednesday’s victory, although the official qualifying criteria has not been announced.

It is also possible that the old, smaller format will be retained for a few more years: Not even Sounders officials were sure in the afterglow of Wednesday night’s win.

“We don’t have the format yet; we don’t have the location,” Garth Lagerwey, the team’s general manager, told reporters. “We’re told, probably February-ish. Probably Middle East maybe.”

Despite the uncertainty, Lagerway, a longtime M.L.S. executive, did little to hide his excitement at the achievement. “We’re going to play Real Madrid or Liverpool, man,” he said. “In a real game.”

Officially, FIFA would only say Thursday that “further details about the FIFA Club World Cup 2022 will be announced in due course.”

An American team has nearly played in the Club World Cup once before. The very first Club World Cup, in 2000, was an eight-team event in Brazil. That year was the last one in which an American team, the Los Angeles Galaxy, won the continental championship. So for the 2001 world event, expanded to 12 teams, the Galaxy was duly entered alongside Real Madrid and other teams from around the world.

But financial concerns and the collapse of a sponsor led the event to be scrapped. It was revived in 2005 in its current format. Too late for the Galaxy. Mexican and Costa Rican teams — to the immense frustration of M.L.S. — have won the title every year since.

Now that the Sounders have broken that streak, they and M.L.S. will hope the Club World Cup — whenever it is held, and whatever it looks like — goes more smoothly.

Tariq Panja contributed reporting.