A newspaper has reported that an undercover investigator met the former Portsmouth player Sam Sodje, who allegedly said he could arrange for players in the Championship to get themselves a yellow card in return for tens of thousands of pounds.
The 34-year-old also allegedly claimed he could rig Premier League games and even said he was preparing to fix matches at next year's World Cup in Brazil.
Portsmsouth said Sodje no longer played for the club at the time of the allegations but they would co-operate fully with any investigation if approached by the authorities.
The report also claimed that the Oldham player Cristian Montano failed to get a yellow card in return for money in a match against Wolves on October 22 and offered to take part in another rigging incident.
Oldham said they would carry out an immediate internal investigation into the allegations.
The Blackburn Rovers striker DJ Campbell was confirmed to be one of the six players who were arrested in December.
Preston North End also confirmed on their website that they had been contacted by the NCA. "There are no suggestions that any offences that might have occurred involved match-fixing. None of our employees has been charged with any offence at this time and until or unless this position changes we will be taking no further action nor making any further comment."
A Football League spokesman said: "We have been made aware that a number of arrests have been made in relation to an ongoing police investigation. We will provide our full co-operation to the relevant authorities."
In a brief statement, the Football said: "The FA has been made aware of developments in relation to an ongoing NCA investigation, including a number of further arrests. We are liaising with the authorities in relation to these allegations. The FA will make no further comment at this time."