Julian Araujo's move from LA Galaxy to Barcelona will not be permitted by FIFA after documentation for the transfer was filed too late, the LaLiga club confirmed on Friday.
Barca and LA Galaxy agreed a fee potentially rising to €4 million for Araujo to move to the Spanish club on Tuesday, a source told ESPN.
However, Barcelona director of football Mateu Alemany said that a "system error" caused the club to miss the midnight deadline at the end of the transfer window by just 18 seconds but he hoped for a review to allow the deal to be concluded.
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A FIFA spokesperson told ESPN on Friday that the deal would not be permitted.
"FIFA can confirm that the transfer of the player Julian Araujo from LA Galaxy to FC Barcelona was not completed in line with the applicable regulations," they said.
Tuesday was the final of the January transfer window in the majority of European leagues and Barca can now not sign anyone else until the summer.
"This is, I think, the second window that we've had some interaction with them (Barcelona) about Julian (Araujo)", Galaxy head coach Greg Vanney said on Thursday after Araujo returned to team's practice.
"The discussion about what a deal would actually look like, started to get really clear and negotiating. So, it was over the last three to four days where those discussions started to pick up and get momentum. And things started to happen fast, hence the reason why it went down to the wire. But it's clearly someone that they've had on their radar because in previous windows they've poked around and asked about him."
It was not the only transfer to miss the deadline, with Hakim Ziyech's switch to Paris Saint-Germain on loan from Chelsea also falling foul of the stated timeframe.
Araujo, 21, was set to sign for Barca's reserve team in the Spanish third tier but the plan was for him to be in and around the first team, who have no recognised right-back after Hector Bellerin joined Sporting CP this week.
Bellerin moved to Lisbon in search of regular football, with coach Xavi Hernandez often preferring to use Jules Kounde, Ronald Araujo, Sergi Roberto and Alejandro Balde out of position rather than field the former Arsenal player.
Therefore, after also touting a move for young Flamengo right-back Wesley, Barca decided to push ahead with their interest in Araujo, who they had also considered signing last summer.
After initially agreeing a loan deal with an option to buy with LA Galaxy, a source close to the negotiations told ESPN "the structure was changed," which led to a delay in getting the documentation ready.
Rather than a loan, Barca were due to acquire 50% of Araujo's rights for €2m with the option to buy another 40% for €2m at a later date, leaving the Galaxy with 10%.
However, there was also a clause that would have allowed Barca to cancel the agreement, in such circumstances rendering the deal effectively a loan, but the source could not confirm if the Catalan club would face a financial penalty for doing so.
Araujo has long been a rising talent with the Galaxy. After spending part of his youth career with the Casa Grande, Arizona-based Barca Residency Academy, he signed with the Galaxy's reserve side in 2018.
He then inked a first-team deal the following season, and since then has made 107 league, cup and playoff appearances, scoring two goals. He has also been a steady contributor to the Galaxy's attack, recording a combined 16 assists over the past two seasons in league play.
At international level, Araujo initially played for the U.S. at various youth levels, including at the 2019 FIFA U-20 World Cup. He even made one senior team appearance for the U.S. before filing a one-time switch to Mexico in October of 2021. He has since made three appearances for El Tri.
Information from ESPN's Jeff Carlisle was used in this report.