As the imminent new CEO of Volkswagen, Porsche chief Matthias Mueller sure has some cleaning up to do.

Volkswagen's already-messy emissions cheating scandal got even messier Friday (Sept. 25), when Germany's transport minister reported that the auto manufacturer also rigged emission tests on roughly 2.8 million diesel vehicles in Germany as well, as reported by Reuters.

This comes after Volkswagen admitted Tuesday (Sept. 22) that 11 million of its vehicles had software installed in them that allowed the auto manufacturer to cheat in United States emissions tests. The next day, Martin Winterkorn quit as the company's CEO, with Mueller (pictured below) expected to be his replacement.

However, the drama kept unfolding, with Volkswagen's scandal deepening.

On Thursday (Sept. 24), German transport minister Alexander Dobrindt announced that Volkswagen had also cheated in tests in Europe, listing the number of affected vehicles in Germany at 2.8 million on Friday. According to reports, Germany might even work with U.S. law firm Jones Day for a thorough inquiry into Volkswagen.

"VW needs to be very open about what has happened, how it was possible that this could happen to make sure that this never happens again in the future," a prominent Volkswagen shareholder told Reuters. "These are priorities that should override all other considerations at the moment."

Amid the scandal, Volkswagen shares continue to take a nose dive, plummeting by as much as 40 percent.

While other shareholders might have preferred to see Winterkorn weather the storm, there's no doubting that Mueller has some serious work to do to change people's perception of the auto manufacturer. Even with a proven track record at Porsche, he'll have plenty of cleaning up to do for seemingly a very long time.