Detective agency Metodo 3 was reportedly used to spy on Barcelona defender Gerard Pique by club officials.
Spanish website El Confidencial is thought to have claimed that the Catalans ordered detectives to follow the 26-year-old when he began a relationship with Colombian singer Shakira in 2010 in order to see if it could damage his form on the pitch, according to The Guardian.
"The club does not wish to comment on this because it has no documentary evidence that this ever happened and, as a result, we deny it," a club spokesman is quoted as saying.
Meanwhile, the couple became parents to son Milan Pique last month.