A British football agent has been released on bail after being arrested as part of a blackmail investigation following an email threat allegedly made to former Chelsea director Marina Granovskaia, according to reports.

The Times reported that the agent, who cannot be identified for legal reasons, sent the message to Granovskaia while she was working on Todd Boehly's takeover of the club. Granovskaia left Stamford Bridge in June, shortly after it was completed.

Police are investigating after the agent allegedly threatened Granovskaia and demanded £300,000 for his role in a high-profile transfer.

'If Chelsea don't pay it then the debt will be on you to pay,' part of the message said, according to The Times. 'I am done trying to be nice to you.' 

The Times reported the agent cited a similar threat to one he had made to another football figure. 'I will make you pay for the way you have been,' he wrote in his email. 'That's not a threat . . . it's a promise. If Chelsea don't pay it's on you . . . see you when I see you.

'I will give you the chance to make things correct if you apologise for your behaviour towards me. If you don't then I promise you I will make you pay for the way you have been with me on a personal and business level. This is not a threat so take it how you want. This is a promise that I give to anybody who f***s/tries to f*** me over in anything in life.'

Marina Granovskaia allegedly received a threatening email from a British football agent

A police spokesman confirmed to the newspaper that a man was arrested in connection with the investigation before being released on bail on September 19.

Granovskaia oversaw Chelsea's recruitment under former owner Roman Abramovich before leaving the club after the £4.25billion takeover by Boehly's Clearlake Capital consortium was completed.

Granovskaia, in her role under Abramovich, had been lauded as 'football's best club director'. 

The Russian-Canadian business executive effectively ran the club on a day to day basis. According to to Chelsea's website, she had 'acted as a representative of the owner at the club and in support of the board of directors' since her arrival in 2010.

Granovskaia was one of several figures to depart the club following Boehly's takeover. Former club chairman Bruce Buck also left, along with chief executive Guy Laurence, as part of an overhaul at Stamford Bridge.

Boehly installed himself as interim sporting director following Granovskaia's departure and oversaw a record £270m spend in the summer.

Chelsea said when confirming Granovskaia was leaving that she would 'remain available to Boehly and the club for the duration of the current transfer window'.