Spain's players gathered on a stage at Madrid's Cibeles Square to meet the fans on Monday when Rodri and Álvaro Morata took the mic and invited the crowds to join the chant "Gibraltar is Spanish".
The Spanish football federation has been hit by another scandal just two days after celebrating one of the most thoroughly deserved victories in football's history.
On Sunday, La Roja won a record-fourth Euro championship after beating England 2-1 in the final in Berlin in a dominant tournament performance studded with seven victories out of seven games.
The Spanish squad was treated to a hero's return when they set foot back on home soil and paraded through the streets of Madrid on Monday to mark the achievement.
The players gathered on a stage at Cibeles Square to meet the fans when Rodri and Álvaro Morata took the mic and invited the crowds to join the chant "Gibraltar is Spanish".
Footage circulating on social media shows most of the Spanish team jumping and singing along.
The crowd's response to Rodri's call appeared to be tepid, but Gibraltar's response came fast.
On Tuesday, Gibraltar's football federation published a statement saying they had filed an official complaint with UEFA over Spain's "unacceptable chanting and songs".
"The Gibraltar FA has noted the extremely provocative and insulting nature of the celebrations around the Spanish men's national team winning Euro 2024," it said, adding that "football has no place for behaviour of this nature."
The episode risks spoiling the season of the 28-year-old midfielder, whose full name is Rodrigo Hernández Cascante.
In 2023-24, Rodri won the Euro championship with Spain - where he was also named player of the tournament - as well as the Premier League with Manchester City, and is now tipped as one of the favourites to win the next Ballon d'Or.
Why is the Gibraltar issue so contentious?
Gibraltar, on the southern tip of Spain, has been a British overseas territory since 1713, when it was handed over as part of a treaty following the War of the Spanish Succession.
With a population of about 35,000 people, it's today the only remaining UK enclave in continental Europe.
Calls for a return of the territory under Madrid have grown exponentially after Brexit.
The UK's exit from the EU created a hard border between Gibraltar and mainland Spain, which made it harder for people and goods to flow.
In recent years, Madrid and London have held 19 rounds of negotiations to try to reach an agreement on the issue. The latest meeting in April did not produce a definitive deal.
In the 2016 Brexit referendum, 96% of voters in Gibraltar supported remaining in the EU.
Spain's Sports Minister Pilar Alegría downplayed the row: "It must be interpreted within the specific context or moment in which it occurred. I believe no one doubts that a country's foreign policy is established by the government".
The controversy comes after a long series of political and diplomatic rows at Euro 2024. UEFA has not yet commented on the episode, but a disciplinary proceeding looks likely.
European football's top body has demonstrated zero tolerance for politically-charged statements and provocations this summer.
Countries like Albania, Serbia and Turkey faced hefty fines during the tournament, and UEFA even banned journalists over nationalist gestures.