Highly placed sources said Rohtagi's opinion is being analysed by the officials handling the probe.
They said the AG's opinion is not binding on the agency but rarely CBI has taken a contrary view.
The sources said a considered view will be taken how to finalise a legally sound charge sheet based on the available evidence in the light of observations of Rohtagi.
Rohtagi had dispatched his opinion saying the available material with CBI is enough to prosecute Dayanidhi and Kalanithi in the Aircel Maxis case.
Meanwhile, Malaysian telecom giant Maxis has written to Directorate of Prosecution, O P Verma, CBI claiming that the deal was done with the full consent of the Aircel Board of Directors.
"Chairman Aircel informed about the Board that the offer price quoted Ms Maxis Communication Berhad is quite attractive...Exchange of correspondence with Mr Sivasankaran in the course of negotiations which will show that Mr Sivasankaran was a willing and that he had obtained the valuation that he so desired or his investment in Aircel," it said.
"While we are not privy to the contents of the subject opinion and usually do not respond to media reports, we are extremely concerned with this turn of events," it said.
The sources said the matter was escalated to the office of the attorney general as there was a difference of opinion between the views of investigation team and the CBI director Ranjit Sinha on charge sheeting Maran brothers in the case.
While the team was of the view that enough evidence was available indicating role of Marans, CBI director Ranjit Sinha differed with the view and highlighted apparent weak points in the draft charges and available evidence.
They said the matter remained pending with then Attorney General G E Vahanvati during the last government.
CBI in 2011 had filed FIR in the case alleging that Dayanidhi Maran as telecom minister had used his influence to help Malaysian business tycoon T Ananda Krishnan acquire Aircel by coercing its owner C Sivasankaran.
It was alleged by Sivasankaran that the then telecom minister had favoured Malaysia-based Maxis group in the takeover of his company and in return investments were made by the company through Astro network in a company owned by the Maran family.
Maran, who has been examined by CBI, has denied all the allegations levelled against him and his family members.
The agency had also sought information from the Malaysian authorities through Letters Rogatory but it did not get satisfactory details, after which the judicial requests were sent again. The reply to second LR is pending.
CBI has named Maran, Kalanithi, Ananda Krishnan, senior executive Ralph Marshall three companies on charges of criminal conspiracy under Indian Penal Code (IPC) and Prevention of Corruption Act.