Lionel Messi and Barcelona will take legal action against Spanish newspaper El Mundo after it released the leaked details of the forward's record-breaking contract on Sunday.

El Mundo published documents relating to Messi's four-year deal, signed in 2017, and gave an intricate breakdown of the €555 million he would receive if all add-ons were met. The report claimed that Messi's contract is the biggest ever signed by an athlete.

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Sources have confirmed to ESPN that Messi will take action against El Mundo and any Barca personnel involved in the leaking of the contract. There are only four copies of the contract -- Messi has one, Barca have another, La Liga has a copy and so does Cuatrecasas, the law firm used by the Argentina international.

Barca, meanwhile, responded by denying any involvement in the leaking of the contract and said they would also take "appropriate legal action" against the newspaper.

"In view of the information published today El Mundo, in relation to the professional contract signed between FC Barcelona and the player Lionel Messi, the club regrets its publication given that it is a private document governed by the principle of confidentiality between the parties," the Catalan club said in a statement.

"FC Barcelona categorically denies any responsibility for the publication of this document, and will take appropriate legal action against the newspaper El Mundo, for any damage that may be caused as a result of this publication.

"FC Barcelona expresses its absolute support for Lionel Messi, especially in the face of any attempt to discredit his image, and to damage his relationship with the entity where he has worked to become the best player in the world and in football history."

According to El Mundo, Messi would receive a maximum of €555,237,619 ($673,919,105) over four seasons, if a series of conditions were met.

Including image rights, the report explains that Messi was paid a €115m renewal bonus and a €77m loyalty bonus split into two payments -- as revealed by ESPN in November.

Messi is also said to earn around €72m annually in addition to add-ons for playing more than 60% of games throughout the course of a season, Champions League progression, winning La Liga or the Copa del Rey and winning FIFA's The Best.

A number of those performance-related add-ons have not been met and it should also be noted that Messi accepted a salary cut when the coronavirus pandemic first affected football last March.

Therefore, he will not earn the full €555m written into the contract, which expires on June 30.

Messi's future beyond then remains unknown. He tried to leave the club last summer but was shut down by then-president Josep Maria Bartomeu.

In a recent interview, he explained that he has not yet made a decision on his future and will decide his next step when the season ends.

Since pushing to leave, Bartomeu has left Camp Nou and a new president will be elected on March 7. All three candidates for the presidency -- Joan Laporta, Victor Font and Toni Friexa -- have expressed a desire to keep Messi at the club.

However, negotiations over a new deal will not be able to begin until March and the new terms will have to correspond with the club's new financial position.

The club's annual accounts, dated August 2020, revealed earlier this month that the Catalan club's gross debt has risen to nearly €1.2 billion.