The sister company of a PR firm that represents David Beckham has confirmed it was subject to a blackmail attempt.
The Daily Mirror reported how a hacker demanded money in return for not publishing hacked emails between Beckham and PR adviser Simon Oliveira. Police are investigating.
The details of the emails have since been published by the British press.
A spokesman for ex-England captain Beckham, 41, said the emails were "hacked", "doctored" and "private".
The hacker is understood to be from Eastern Europe or one of the former Soviet republics.
Through a lawyer, the hacker approached Doyen Sports, which is based in Portugal and is a sister company of Doyen Global, the sports and entertainment agency co-founded by Mr Oliveira.
Doyen Sports was given a clear indication that the individual had hacked "other sports agencies and sport accountancy firms".
Those close to Beckham, the former Manchester United and Real Madrid star, said the individual was connected to the website Football Leaks - the sporting equivalent of whistle-blowing site Wikileaks.
Doyen Sports refused to pay and informed Portuguese police, who opened an investigation into the matter early last year.
Police in Portugal have confirmed to the BBC they are investigating a case related to Football Leaks.
It is understood the hacker passed his material to European Investigative Collaborations, a network of journalists, who spent several months digesting it, before distributing it to several European websites last week.
Tony Gallagher, editor-in-chief of the Sun newspaper, came across the allegations about Beckham last Friday evening on social media.
The newspaper printed the details of the emails on Saturday.
Emails Beckham had allegedly written appeared to reveal his frustration at missing out on a knighthood in 2013 and his irritation that other celebrities had received honours.
One allegedly said: "It is a disgrace to be honest and if I was American I would of got something like this 10 years ago."
There were also financial details of his work with the children's charity Unicef, of which he is an ambassador.
Beckham has not commented personally, but a spokesman for the star said: "This story is based on outdated material taken out of context."
Unicef said it could not comment on the emails, but in a statement said: "As well as generously giving his time, energy and support to help raise awareness and funds for Unicef's work for children, David has given significant funds personally."