Barcelona will take legal action against the Spanish newspaper El Mundo after it published details on Sunday of Lionel Messi's current contract, which it says is worth up to 555 million euros ($674 million) over four years.
Barca responded by also insisting they were not responsible for the leak, although the club did not deny the details of the report.
El Mundo say the deal signed by Messi in 2017 is the "largest in the history of sport" and called it the "colossal contract that ruins Barcelona".
The 33-year-old could end up collecting a maximum of 555,237,619 euros before it expires on June 30 this year, if all conditions were met.
With six months left of the deal to run, "the player has already earned 511,290,052 euros, almost 92 per cent of the possible total", the report claims.
The leak comes as Barcelona are wrestling with a dire financial situation, worsened by the pandemic, and with Messi's future still up in the air, given the striker can leave the club for free this summer.
"In view of the information published today in the newspaper 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," said Barcelona in a statement.
