Benfica president Luís Filipe Vieira has been arrested for alleged fraud, local media has reported.
According to these reports, Vieira's home, office as well as the Novo Banco bank were searched as part of an investigation into possible financial irregularities.
Portuguese legal authorities said four people had been taken in for questioning as part of a probe into fraud.
Portugal's Public Prosecution Service said in a statement that they were investigating "deals and financings totalling more than €100 million, which may have resulted in heavy losses for the state and some of the companies".
The investigation reportedly stretches back to 2014 and possible offences include "breach of trust, aggravated fraud, forgery, tax fraud and money laundering," it added.
In November, the country's general prosecutor's office carried out series of raids, including at the premises of Benfica.
Prosecutors said they were investigating "a range of cases, all linked to professional football", adding that they were related to sporting and financial partnerships, the acquisition by clubs of players' sporting rights and "loans agreed with a Singapore national".
Last October, real estate businessman Mr Vieira was re-elected president of the 37-time Portuguese champions extending a reign that began in 2003.
