Chidambaram was charged with giving the Foreign Investment Promotion Board (FIPB) clearance to the 2006 Aircel-Maxis deal instead of referring the matter to the cabinet.
CBI sources said Chidambaram was recently asked to give a statement in connection with the case as he was competent for giving sanction only up to Rs.600 crore and the Aircel-Maxis deal was approximately of Rs.3,500 crore.
The sources said the matter should have been referred to the Cabinet Committee on Economic Affairs (CCEA) as foreign investments above Rs. 600 crore can only be cleared by this cabinet panel headed by the prime minister.
The agency had informed the Special CBI court that how this clearance was given is still under investigation.
"We have not concluded the probe on this aspect yet," CBI prosecutor K.K. Goel had told the court.
Chidambaram had said in September that the file regarding the case was put up before him by officials and he approved it "in the normal course".