Piech reportedly told German newspapers that he had raised concerns over the emissions scandal in March 2015, six months before the issue became public.
Volkswagen has threatened to sue former chairman Ferdinand Piech over recent comments he allegedly made to German media.
Piech allegedly told German prosecutors that he had informed VW Group supervisory board members about the US emissions investigation in March 2015, according to Der Spiegel. He was allegedly informed of the inquiry via former Israeli ambassador Avi Primor.
The former chairman reportedly claimed that he confronted Winterkorn after receiving the tip, but the then-CEO allegedly claimed that VW had received no notification from US authorities of an emissions investigation.
VW did not publicly acknowledge the EPA's inquiry until September of that year, prompting Winterkorn's resignation within days. Piech's allegations essentially accuse Winterkorn and others of attempting to brush the scandal under the rug for six months and keep investors in the dark.
"The Supervisory Board of Volkswagen AG emphatically repudiates the assertions made by Ferdinand Piëch as reported recently in the media," the automaker said in a statement.
The company claims law firm Jones Day already investigated Piech's account in detail, but "no evidence was forthcoming indicating the accuracy of these allegations, which were classified as implausible overall." Other affected board members have all denied the assertions.
"The Board of Management will carefully weigh the possibility of measures and claims against Mr. Piëch," the statement added, without elaborating.