Police have arrested three people in connection with a second investigation into football spot-fixing following allegations that a player rigged a Championship game in return for cash.
The National Crime Agency (NCA) confirmed that it had acted on information passed on by the Sun on Sunday newspaper.
The tabloid reported that an undercover investigator met ex-Portsmouth player Sam Sodje, who allegedly said he could arrange for footballers in the Championship to get themselves a yellow card in return for tens of thousands of pounds.
The 34-year-old also claimed he could rig Premier League games and even said he was preparing to fix matches at next year's World Cup in Brazil, the newspaper reported.
Portsmouth FC spokesman Colin Farmery said: "If these serious allegations are true then we are extremely shocked and saddened by them, as match-fixing of any type goes to the heart of the integrity of the game.
"The player in question no longer plays for the club and we have not been contacted by the authorities, but of course we would cooperate fully with any inquiry."
It was also reported that Oldham Athletic player Cristian Montano failed to get a yellow card in return for money in a match against Wolverhampton Wanderers on October 22 and offered to take part in another rigging incident .
Oldham said in a statement: "Oldham Athletic Football Club has been made aware of the incident and allegation surrounding one of its players, Cristian Montano. The club will commence an immediate internal investigation to establish all the relevant facts of the case.
"The club is co-operating with other agencies in this matter and cannot comment on specific facts at this stage. The club will not be issuing any further statements at this time."
An NCA spokeswoman said: " An active NCA investigation is now under way and we are working closely with the Football Association and the Gambling Commission.
"Three people are in custody and are being questioned by NCA officers. We cannot comment further at this stage."
The NCA is already carrying out a separate investigation into an alleged international illegal betting syndicate.
Michael Boateng and Hakeem Adelakun, both 22, were charged last week with conspiracy to defraud contrary to common law.
The pair, who played for Conference South club Whitehawk FC in Brighton, were dismissed by their club and will appear in court on Wednesday.
Two other men, Chann Sankaran, 33, from Hastings, East Sussex, and Krishna Sanjey Ganeshan, 43, from Singapore, were charged last month with plotting to defraud bookmakers and will also appear in court this week.
Speaking about the latest reports, Football League chief executive Shaun Harvey said: "We treat any allegations of criminal activity in our competitions with the utmost seriousness.
"Given that there is an ongoing police investigation into this matter, we cannot comment further at this time. Although, we would encourage anyone with any evidence to report it to the police.
"We will be giving our full assistance to the police during their investigation."
In a statement, the Football Association said: "The FA is aware of the National Crime Agency investigation and is working closely with the NCA and other authorities. We will make no further comment at this time."
A Gambling Commission spokesman said: "The Gambling Commission has responded quickly in supporting this ongoing National Crime Agency investigation and continues to liaise with both the NCA and the Football Association."