Hackers reportedly demanded one million euro from the sports agency representing David Beckham, leading to the leak of a series of the star's personal emails.
Police in Portugal, where Doyen Sports has an office, have been investigating the attempted blackmail for a year.
Beckham was not the explicit target of the hack, a source told the Daily Mirror, but was "caught in the crossfire".
A source said: "They approached by email and attempted to meet via another third party. They said we have all this information and you have to pay up. It was blackmail, pure and simple."
A representative for the former England captain dismissed the contents of the messages, which were published on Friday, as "outdated material taken out of context from hacked and doctored private emails from a third-party server and gives a deliberately inaccurate picture"
The leaked emails included Beckham reportedly lambasting the honours committee and complaining with reference to his charity work.
He is said to have questioned Katherine Jenkins' OBE, referencing a past admission that she had taken drugs.
In response a representative defended Jenkins, issuing a "fact sheet" listing her charity work and success in the music industry.
He said: "With regards to the taking of coke which Katherine has courageously publicly admitted with great honesty - this was when she was in her early 20s still a student - over a decade before she was awarded her OBE and started her recording career."
Other emails reportedly saw Beckham react negatively to a suggested donation to Unicef, of which he is a Goodwill Ambassador.
The charity said: "Unicef has become aware of media reports relating to 7: the David Beckham Fund for Unicef.
"Some reports relate to alleged private correspondence between our ambassador and other parties, which we have not seen and cannot comment upon."
It added: "We are extremely proud of the 7 Fund and all it has achieved for children."
On Sunday Beckham's eldest son Brooklyn posted a picture of the former footballer on Instagram, sitting at a dinner table cuddling his daughter Harper.