The voluntary payment - which the club says is a gesture to "defend the club's reputation" - comes as investigations continue into allegations of tax evasion.
Brazilian Neymar arrived at Camp Nou in the close-season from Santos for a reported fee of €57.1m, although allegations subsequently surfaced that the figure was much higher.
The Spanish courts have since opened legal proceedings over the affair, but in a statement on their official website on Monday, Barca once again protested their innocence and insisted that they will mount a legal defence – as well as revealing the voluntary payment which, the club said, has been made “given the existence of a possible divergent interpretation of the exact amount of tax responsibility arising from the signing.”
"Following the opening of legal proceedings for alleged tax irregularities relating to the different payments made during the signing of the player Neymar da Silva Santos Jr, the Futbol Club Barcelona board of directors has met at the club offices and unanimously reached the following agreements," the statement read.
"The board denies the existence of any tax-related crime in relation to the fiscal obligations arising from the signing of the player. Throughout the process, the club was receiving expert advice and at every moment the club's auditor was informed and had access to all the documentation concerning the negotiations.
"As we have done so far, the club will continue to give maximum collaboration to the Law Courts in order to clarify the facts of the case.
"The club will present a legal defence in the case opened against it and members can be assured that the club has always acted within the law and that the board will defend the club's reputation – one of the most emblematic in our country – until the final consequences and in whatever legal context required.
"We wish to make clear that FC Barcelona has always fulfilled its tax obligations, both in terms of time and method, and has enjoyed close collaboration with the Spanish tax authorities. FC Barcelona has no tax debts.
"The board again insists that in relation to this signing, the club has scrupulously fulfilled its fiscal obligations in line with its awareness at the time of the contracts and agreements signed in good faith.
"Given the existence of a possible divergent interpretation of the exact amount of tax responsibility arising from the signing and to defend the club's reputation and good name, FC Barcelona has this morning made a complementary tax declaration of a total of 13,550,830,56 euros (thirteen million, five hundred and fifty thousand, eight hundred and thirty euros and fifty-six cents) to cover any potential interpretation made concerning the contracts signed in the transfer process for Neymar, although we remain convinced that the original tax payment was in line with our fiscal obligations.
"This voluntary contribution should not be understood as in any way affecting the club's right to have its tax obligations in this matter determined by the competent authorities, concerning which the club reserves the right to further action."
