FIFA president Gianni Infantino says he will block any attempt to stage Girona and Barcelona's La Liga match in the United States next year.
Both clubs have agreed in principle to the proposal to stage a game in Miami in January as part of a 15-year agreement between Spain's top division and Relevent Sports.
La Liga president Javier Tebas has met with serious opposition since putting forward the proposal, with the Royal Spanish Football Federation (RFEF) and Association of Spanish Footballers (AFE) publicly against the plans.
Infantino has now added world football's governing body to the list of those who believe the match must not be staged outside Spain.
"FIFA will not authorise the playing of a match either in the United States or in any other location that isn't the stadium of Girona," Infantino said at a news conference.
"The FIFA Council has addressed the subject, and we stress that official matches of national leagues should be held in the country itself.
"As FIFA president, I announce that the organisation is against La Liga's idea and will forbid Girona-Barca to be held in the United States or any other country that isn't Spain."
AFE president David Aganzo said of the proposals back in August: "The players are outraged, very surprised, and are all against it. It's unanimous.
"The players don't want to play overseas. Things have to be done in a more coherent way and with common sense.
"A decision of this magnitude, that affects players, referees and fans, was taken unilaterally and is a lack of respect.
"I have information that there are certain clubs that are in favour [of strike action] and others against this, but I represent the players.
"We need to sort this out with the union, and we will tell them all of our problems. If, from then on and after a few days, they don't answer, then we will have to solve the situation.
"We are going to try to see that it doesn't reach that extreme. But we are willing to go right to the last option if it is necessary."
