Hostility that boiled over on-pitch between Real Madrid and Barcelona last week threatens to undermine the Spanish national squad ahead of the Euro 2012 championship, Malaga and Spain midfielder Santiago Cazorla warned on Monday.
"The situation in the national squad is tense. However much we want to avoid it, these cup competitions have an influence on relations," he was quoted as saying by newspaper La Nueva Espana, referring to Wednesday's heated Supercopa tie.
"The atmosphere is still very good" in the national team, he added, but warned: "if this kind of problem continues it could have an influence and that could end up being very damaging."
Wednesday's second-leg Supercopa clash between the arch-rivals in Barcelona degenerated into a scuffle between rival players and staff, with Real Madrid's manager Jose Mourinho poking a Barcelona assistant coach in the eye.
It was the latest eruption in recent seasons of tense relations between the historic rivals, whose players formed the bulk of Spain's winning team at the World Cup in South Africa last year.
Spain coach Vicente del Bosque, a former manager of Real Madrid, said in June that the rivalry has left "wounds" on the national team that need to be healed.
His squad are well placed to qualify for next year's Euro 2012 finals in Poland and Ukraine having amassed a maximum 15 points from five games and next play Liechtenstein on September 6.
In its last international match, Spain lost 2-0 to Italy in a friendly on August 10.