Former Volkswagen chief executive Martin Winterkorn received emails about the company's emissions crisis one year before it became public, the company said in a statement Wednesday.

In the statement published on its website, Volkswagen also said it would defend itself against legal action by shareholders over the scandal, in which it emerged that the carmaker was cheating on emissions tests.

Winterkorn resigned after revelations that millions of Volkswagen vehicles had been fitted with a "defeat" device to cheat emissions tests.

He received a memo in May 2014 and was present at meetings where the issue was discussed before it became public, but it "did not initially receive particular attention" from Volkswagen management, according the document.

Volkswagen is also facing legal action in a class-action lawsuit in the United State that accuses the German auto giant of major damages to the environment and to car owners.

Volkswagen has admitted installing the cheat devices into 11 million vehicles worldwide, plunging the group into its deepest-ever crisis with potential fines and legal costs running into tens of billions of euros.