Jean-Marie Messier, former chief executive of French media giant Vivendi Universal, has left police custody.
Mr Messier was ousted from Vivendi in 2002
Mr Messier was being questioned as part of an investigation into "financial misappropriation", Paris police said.
The arrest followed a probe into Vivendi ex-finance chief Guillaume Hannezo launched earlier this month.
Under Mr Messier, Vivendi ran up huge debts to fuel acquisitions, before the corresponding losses persuaded shareholders to oust him in July 2002.
The investigation centres on allegations of possible insider trading in Vivendi shares.
For months, judges - who in France oversee police investigations - have been looking at sales of Vivendi stock in December 2001, shortly before a sharp fall in the company's share price.
During that period, Vivendi was struggling to contain the debts run up as a result of Mr Messier's strategy to turn the utilities-focused group into a media powerhouse.
The shares had been bought back by the company in late September and early October, amid the worldwide slide in share prices which followed the 11 September attacks on the US.
That, investigators believe, could violate French stock market rules banning share buybacks in the 15 days before companies report their results.
The inquiry already encompasses three other executives aside from Mr Hannezo.