Volkswagen is considering legal action against Martin Winterkorn, its former chief executive, for negligence over his part in the "Dieselgate" emissions scandal, says a spokesman for the company.
Winterkorn is already facing criminal charges in the US over his role in the affair, although the case is unlikely to go to trial as Germany does not extradite its citizens.
But a civil lawsuit from VW could potentially ruin him, according to German legal experts, who said the company could seek damages of more than €100 million ($170m).
"The investigation has been going on for quite some while and is conducted independently of the authorities' investigation," said Michael Brendel, a spokesman for the VW supervisory board.
Winterkorn was VW chief executive in 2015 when it emerged that the company had rigged software on 11 million cars to enable them to cheat emissions tests. He initially tried to cling on to his position, but resigned five days later saying he was "utterly sorry".