On Wednesday, El Mundo released a series of requests Messi made to the club to renew his deal at Camp Nou as he moved into the final year of his terms.
Messi wanted his release clause cut down to a symbolic €10,000, private boxes at Camp Nou for his and Luis Suarez's families, guarantees that deferred wages would be paid back to him and backdated commission payments to be paid to his brother Rodrigo for his work as an agent.
"In relation to the information published in El Mundo under the title 'Barca Leaks, the club's secret files', Barcelona express indignation at the intentional leaking of information that is part of a legal process," the Catalan club said in a statement.
"The club regrets that the media in question boasts of having 'access to a huge number of documents and emails that are part of the Barcagate investigation' when this information is yet to be shared.
"In any case, the article in question makes public documents that have nothing to do with the ongoing case and their use is an affront to the reputation and confidentiality of the club. For that reason, and with the aim of protecting Barcelona's rights, the club's legal department are studying the legal measures that need to be taken."
Barcagate is an ongoing legal case relating to third-party payments, breaching internal protocols and smear campaigns against club legends involving the previous president Josep Maria Bartomeu and his board of directors.
Messi is not part of that case, nor is his previous contract subject to any misdemeanours, but emails exchanged during talks over a renewal were seized by police as they gathered information for the Barcagate case.
Those emails subsequently ended up in El Mundo on Wednesday.
The Spanish newspaper's revelations detail how Messi wanted a three-year deal until 2023 with a €10 million signing bonus and a unilateral option to extend the contract until 2024.
Messi was willing to take a 20% deferral to his annual salary -- which was around €70m, as revealed by El Mundo in a previous leak -- in 2020-21, but wanted guarantees he would be paid the deferred sums back in the following years with added interest.
Later that same year, after an 8-2 defeat to Bayern Munich in the Champions League, Messi filed a transfer request via a burofax, a form of recorded delivery, but it wasn't until 2021 that he left for Paris Saint-Germain on a free transfer.
In 2021, he had agreed the terms of a new contract with new president Joan Laporta, including a 50% pay cut, although Barca could not afford to register it with LaLiga, while his requests the previous year were never green-lighted by the previous president Bartomeu.