Spanish footballing giants Barcelona and Valencia on Monday rejected allegations on a Spanish radio station that they may be involved in doping.
Barcelona "wishes to publicly express its total indignation at these unfounded references which link the club to doping practices" while Valencia described the allegations on the Catholic radio station Cadena Cope as "false."
Cadena Cope on Sunday quoted a "representative" of Real Madrid, who was not identified, as saying the club planned to "ask the Spanish football federation for serious anti-doping controls."
The private radio station said Real "goes even further. Real Madrid does not understand that Eufemiano Fuentes worked in the past for a club in the first division, specifically Valencia, curiously when it won two championships," in 2002 and 2004.
Fuentes, a doctor, was one of six people charged last December with trafficking offences in an athletics doping network after a police investigation known as Operation Galgo.
"Real Madrid does not understand either that other doctors of a doubtful reputation work for Barcelona FC."
Barcelona said in a statement it "is demanding an immediate rectification and wishes to let it be known that its legal department is studying possible legal action to defend the club's honour, alongside that of its coaching staff, players and medical staff and is prepared to take such action to its final consequences."
Valencia said it had "never worked" with Fuentes or been "advised directly or indirectly by him."
A spokesman for Real Madrid - who have looked on enviously in recent years as Barcelona has dominated the league and flourished in Europe winning the Champions League twice since Real's last victory in 2002 - declined to comment on the Cadena Cope report.