( CNN ) -- Football club Barcelona paid 13.5 million euros ( $ 18.5 million ) in additional taxes on Monday , while denying any fiscal `` irregularities '' in its purchase of Brazilian superstar Neymar , which is now under investigation by a court . FC Barcelona announced the surprise payment on its website , which it called `` voluntary , '' just four days after a judge at Spain 's National Court in Madrid filed preliminary charges against the fan-owned club for alleged tax fraud in the Neymar deal . `` The board ( of Barcelona ) denies the existence of any tax-related crime in relation to the fiscal obligations arising from the signing of the player ( Neymar ) , '' the club 's website said . `` 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 . '' Last Thursday , Judge Pablo Ruz expanded his investigation against the club , as requested a day earlier by a prosecutor , who alleged the club avoided paying 9 million euros ( more than $ 12 million ) in taxes on Neymar 's signing and transfer , corresponding to contracts signed in 2011 and 2013 . The judge is already investigating whether a former Barcelona president committed financial irregularities in the signing of Neymar . The club said on its website Monday : `` 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 . '' The reason , the club added , was `` 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 . '' Judge Ruz said in his writ last Thursday that the investigation would include a look at an alleged `` contract simulation presumably carried out by the parties which signed the contracts . '' The expanded investigation would hold FC Barcelona responsible as an entity or business enterprise if found guilty of tax fraud , said a National Court spokesman , who by custom is not identified . The judge ordered Spain 's tax collection agency to examine FC Barcelona 's tax filings for 2011 , 2012 and 2013 , the writ said . Neymar joined Barcelona in June 2013 , with his father -- who doubles as his agent -- having entered into an initial contract with the Spanish giants in late 2011 . Barcelona 's former president , Sandro Rosell , who resigned last month after a judge agreed to investigate a lawsuit against him for alleged irregularities in the Neymar deal , has denied any wrongdoing . Ruz began the investigation last month after a legal complaint from one of the club 's members . Prosecutor Jose Perals last Wednesday formally asked the judge to expand the investigation . In his writ , Perals alleges that he 's `` become aware of a series of economic transactions by the club , and in favor of various companies , related to the signing of Neymar da Silva Santos Jr. , based at times on simulated contracts . '' The investigation originally came after season-ticket holder Jordi Cases complained that the amount paid to bring Neymar from Brazilian side Santos was more than the reported fee of 57.1 million euros . A day after Rosell resigned , the club released figures that showed that Barca actually paid 86.2 million euros for Neymar . Cases ' lawyer , Felipe Izquierdo , earlier told CNN that other Barcelona executives , still working at the club after Rosell 's resignation , also allegedly signed some of the contracts that brought Neymar to the club . Barcelona has told CNN that one of those signatories was former club VP , and now President , Josep Maria Bartomeu . Piers Edwards and Chris Murphy contributed to this report .
Barcelona pay $ 18.5m in tax four days after judge files charges for alleged tax fraud . Tax fraud allegations came as Spanish judge expanded inquiry into controversial Neymar deal . Score: 6