The agency also said investigation against Essar Group was still on and it will take another two weeks to complete it.
CBI, which filed a fresh status report in a sealed cover about the progress of the investigation, said the preliminary inquiry on the alleged involvement of Maran in 2G scam has been completed and letters rogatory have been dispatched to Mauritius.
"The preliminary inquiry with regard to Maran has been concluded and FIR has to be registered against everyone. A few more days needed for the FIR and can be lodged by month-end," senior advocate K K Venugopal, appearing for CBI, told a bench of justices G S Singhvi and A K Ganguly.
Venugopal was referring to the probe into the sale of Aircel to Malaysia-based Maxis Group.
Maran was the telecom minister between May 2004 and May 2007. He was forced to resign as the Union textiles minister in July this year after CBI said it was investigating a complaint against him filed by C Sivasankaran who owned Aircel in 2006.
The senior advocate said CBI has examined Sivasankaran and during the probe it has been found that "undue favour" was shown to the foreign firm and the allegation of quid pro quo arrangement in the dealing has been probed.
"The money involved is about Rs 549 crore," he said without reading out the details of the report on the issue.
A top executive of the Maxis group, Ralph Marshall, CEO of Astro, which invested in Sun TV, owned by Marans, and also a board member of Malaysia-based Maxis, was questioned this month by CBI in connection with alleged irregularities in spectrum allotment during the tenure Maran as telecom minister.
CBI had also questioned Executive Director of Apollo Hospital Suneeta Reddy on the alleged role of Maran in the takeover of Aircel by Maxis.
However, when the bench wanted to know about the status of the probe on Essar group, Venugopal said "investigation is still on".
During the last hearing, CBI had rubbished the reports that Maran has been given a clean chit in the scam.
CBI had on July 6 charged Maran in the Supreme Court with "forcing" a Chennai-based telecom promoter to sell his stakes in Aircel to Maxis in 2006.