German prosecutors have accused Mr Winterkorn, and another former board member, of withholding information from investors about VW's emissions scandal.
Mr Winterkorn resigned last September following revelations that the firm cheated US diesel car emissions tests.
But VW said the prosecutors have offered "no new facts or information".
Volkswagen has already said in response to an investor lawsuit that it met its disclosure obligations.
Mr Winterkorn said at the time of his resignation that he was "not aware of any wrongdoing on my part".
Instead, he said that his resignation had been in the best interests of the company.
The German prosecutor's office in Braunschweig said that the investigation focused on "sufficient real signs" that Volkswagen had not alerted investors as soon as they were aware of the possible financial damage of the emissions manipulation.
The firm officially notified investors on 22 September last year.
Prosecutors did not name the second former board executive being investigated.
Germany's financial watchdog, the Federal Financial Supervisory Authority, requested the probe, prosecutors said.
On Monday, Europe's largest carmaker, said in a statement: "Today's press release from the Braunschweig public prosecution service does not cite any new facts or information on any serious breaches of duty by the members of the Board of Management now accused.
Last year, US regulators discovered that VW cars were fitted with software that could distort emissions tests.
The German giant subsequently said 11 million cars worldwide were affected.
Last September Volkswagen admitted to installing so-called defeat devices in 11 million cars worldwide.
Regulators found the defeat device enabled VW cars to appear less polluting during tests than they would while driving normally.
Former Volkswagen boss Martin Winterkorn is under investigation in Germany for alleged market manipulation.