During the investigation, which began about 15 days ago, the CBI searched and collected documents from Delhi-based authorities. All India Football Federation they said in several Indian football clubs.
Under the scanner, they said an alleged Singapore-based matchmaker had a role in rigging the results of the matches.
Authorities declined to provide any details about the suspects named in the preliminary investigation and details of the allegations, as it could hinder the investigation, which is in its infancy.
They said the agency has received some documents, while others are still awaited.
The agency also said it sought the cooperation of several Indian football clubs to participate in the investigation.
Citing the law, the CBI said it could not subpoena, arrest or interrogate as part of a preliminary investigation.
The central investigation agency is dependent on the cooperation of stakeholders during the preliminary investigation and registers an FIR when it has material that indicates a crime at first glance, they said.