A Spanish court has ordered LaLiga to accept Gavi's new contract at Barcelona and his registration into the first team.
The court's ruling said a failure to enroll Gavi with the first team before the January transfer window closes on Tuesday "would imply the player's free agency and therefore cause serious, irreparable damage to Barca."
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LaLiga announced they will appeal the decision and that it "is unaware of the contents of the main legal claim."
"This provisional measure has been adopted without LaLiga having had the opportunity to present its arguments," the statement said. "LaLiga, of course, will abide by the provisional measure, but will appeal it, considering that there are sufficient factual and legal grounds for the Court to remove it."
Barca tweeted a photo of Gavi with the No. 6 jersey on Tuesday -- the same number worn by Barca manager Xavi Hernandez during his playing days at Camp Nou.
Gavi, 18, signed a new deal with the Catalan club in September, extending his stay at Camp Nou until 2026, but those terms have not been registered with LaLiga and he technically remains a youth-team player.
Barca attempted to register the contract last week but LaLiga refused to do so, with league president Javier Tebas explaining on Monday that as a multi-year contract they did not have enough space within their salary limit to do so beyond this season.
"The No.10 Commercial Court in Barcelona has made a decision agreeing the adoption of the unusual, provisional measure consisting of 'urging the Spanish Football League (LFP)' to do all that is necessary so that Gavi can be registered as a first-team player before the close of the winter transfer window," Barca said in a statement Tuesday.
"The decision recognises the authority of the LFP and considers there is a principle of legitimacy in Barca's claim and that the failure to register the player before the end of the transfer window would imply the player's free agency and therefore cause serious, irreparable damage to Barca."
Barca coach Xavi Hernandez said the ruling was "great news" for the club but that he never feared Gavi, who has already made 75 appearances for the senior side, would walk away for nothing.
Defender Ronald Araujo's new contract, agreed last April, is also yet to be registered with LaLiga, although the Uruguay international is already signed up as a first-team player.
Meanwhile, Barca continue to scour the market for loan signings before the transfer window closes.
Sources have told ESPN that Anthony Elanga, Sofyan Amrabat and Julian Araujo are all options and Xavi confirmed there could be arrivals on Tuesday, with defender Hector Bellerin set to join Sporting CP after "asking to leave" in search of regular football.
"We are in a situation where we depend a lot on the financial situation once again," Xavi said in a news conference. "Hector will leave and I want to thank him because he has been an example and always shown a good attitude.
"So now, with the departures of Gerard [Pique], Memphis [Depay] and Hector, I think a signing would be very welcome. In what position? We don't know. It is a very difficult market to work in but we are open to signings.
"We won't sign for the sake of signing, though. I am happy with the squad I have, but if the right opportunity comes up, we will take it. If not, I have faith in the B team and the youth team."