The dedicated marathon runner (seen in centre) deftly avoided reporters as he left the Central Bureau of Investigation headquarters in New Delhi and was driven away in a white Indian-made Ambassador car.
Ambani, who has an MBA from the University of Pennsylvania's Wharton School and whose empire includes No 2 cellular carrier Reliance Communications (RCOM), has not been charged.
On Sunday, RCOM accused their telecoms rivals of "the brazen hijacking" of the 2G spectrum (airwaves).
"It is unfortunate that a malicious campaign of disinformation, falsehoods and calumny is being spread by RCOM's telecom industry competitors and corporate rivals, to put up a smokescreen and cover their own unprecedented irregularities," said Syed Safawi, CEO of RCOM's wireless unit.
One of those rivals, Bharti Airtel Chairman Sunil Mittal, told the Business Standard newspaper in an interview this week telecom operators "should shut their mouths" and let investigators do their job.