Catalan police have arrested four people - including former president Josep Maria Bartomeu - after raiding Barcelona's offices in a search and seizure operation, adding to the club's turmoil less than a week before their presidential elections.
The operation was related to last year's "Barcagate," in which club officials were accused of launching a smear campaign against current and former players who were critical of the club and then-president Bartomeu.
Police did not say who was taken into custody but presidential candidate Joan Laporta confirmed Spanish media reports that Bartomeu was among those detained.
"We are deeply saddened by these events that cause enormous harm to the image of our club," Laporta said.
Among those the Spanish media claimed were detained were club CEO Oscar Grau and legal department chief Roman Gomez Ponti.
Jaume Masferrer, Bartomeu's former chief of staff, also was allegedly detained.
Authorities spent several hours at the team headquarters searching documents and talking to employees.
"The investigation, which has been going on for almost a year, is still ongoing," the police said in a statement.
The club, mired in debt of more than 1.1 billion euros ($A1.7 billion), said it offered "full collaboration to the legal and police authorities to help make clear facts which are subject to investigation".
It added the case was related "to the contacting of monitoring services on social networks".
The club did not mention Bartomeu.
A text message sent to Bartomeu was not immediately answered.
Laporta, one of the three presidential candidates in elections on Sunday, said the news of Bartomeu's detention was "shocking" and "not good" for the club, but stressed that the former president deserved the "presumption of innocence".
Laporta was Barcelona's president a decade ago and, like Bartomeu, also faced a no-confidence vote during his time in charge.
Barcelona had denied accusations that it hired - and overpaid - a company to make negative comments about its own players and opponents on social media in order to boost the image of senior club officials.
Some of the figures supposedly included players such Lionel Messi and Gerard Pique, as well as former coach Pep Guardiola.
The club later released an independent audit report showing that there was no wrongdoing.
Bartomeu and his board of directors resigned in October amid fallout from the controversy surrounding Messi - with a caretaker board in charge since then.
Australian Associated Press
