The four, who had been arrested yesterday as part of a Garda 'Operation Brookweed' day of action, were released without charge.
A file will now be prepared for the Director of Public Prosecutions. One man remains in Garda custody this morning.
Ten men aged between their 20s and 60s had been questioned at stations in three different counties, in relation to the massive probe by the Garda National Economic Crime Bureau (GNECB) that has been ongoing since 2019.
The investigation is focusing on games involving one club, and many of the arrested men had connections to this football team.
Seven of the men arrested in a series of dawn raids yesterday in connection with an ongoing investigation into alleged match fixing in the League of Ireland are footballers, or former footballers.
Some are even due to have involvement in significant football fixtures across the country in the coming days.
Two are still playing football in the League of Ireland. Five of the arrested men have retired from playing football.
Gardaí are satisfied that the alleged betting scam is not linked to wider organised criminal gangs.
Five of the 10 men had earlier been released without charge and a file will be prepared by gardaí for the Director of Public Prosecutions (DPP).
The GNECB investigation began after gardaí received a complaint in 2019 in relation to irregular betting patterns.
The bureau has been working on the case for almost three years.
A source with knowledge of the case said bets may have been placed from other countries on the outcome of games in an attempt to disguise the bets.
“What has been looked at very closely is all kinds of suspicious bets in the course of a number of matches – including goals scored, goals conceded, fouls, the quantity of corners and other bets such as the actual outcome of the games,” a senior source said.
“This has been a highly complex investigation in which there have been a number of phones seized and then analysed, and there has been a massive trawl of gambling records.”
It is understood that two games in particular played in 2019 have been the focus of the probe.
“But the indications are that this went back three years before 2019, and that is being actively looked at,” the source said.
As part of the planned operation in the Southern Region and Dublin Metropolitan Regions, it emerged yesterday that the 10 men were arrested and a number of residential properties were searched under Operation Brookweed.
Gardaí said the operation was supported by staff attached to the Limerick and Cork City divisions.
Investigators said the men were arrested on suspicion of the offence of Conspiracy to Defraud contrary to Common Law and were detained under Section 4 of the Criminal Justice Act 1984 at various stations in the Southern Region and Dublin Metropolitan Region.
Gardaí said the operation stemmed from an investigation carried out by detectives attached to the Anti-Bribery & Corruption Unit in 2019, following reports of suspected match fixing received from the FAI and UEFA.
In a statement, the FAI said: “The Football Association of Ireland notes the latest developments in the Garda enquiry into alleged match fixing.
“The FAI, in conjunction with UEFA, remains committed to a zero-tolerance policy on match fixing. As this is now a legal matter, we will be making no further comment.”
Discussing the operation, Detective Superintendent Catharina Gunne of the GNECB said: “Match fixing and corruption is a threat to all sports at all levels and undermines public confidence in the fairness of sport.”
He added: “It can allow organised crime to infiltrate sport in order to use it to make illicit gains or launder proceeds of crime.”