Volkswagen is preparing for additional costs relating to the German automaker's emissions scandal, chief executive Matthias Mueller has told CNBC. To date, the company has said it has set aside 6.7 billion euros ($7.3 billion) to fix the vehicles capable of cheating emissions tests, and Mueller has previously said this amount should be enough.

New Volkswagen Group Chairman Matthias Mueller speaks to the media with Volkswagen Work Council head Bernd Osterloh and Lower Saxony Governor Stephan Weil (both not pictured) while standing at the assembly line of the Volkswagen factory on October 21, 2015 in Wolfsburg, Germany. Getty Images

However, speaking to CNBC Monday via a translator, the CEO of the stricken German carmaker said the company was working on the assumption that additional provisions would be needed. Mueller said that the provisions "need to be increased, but to mention figures at the moment would be to speculation." Volkswagen originally admitted on September 18 last year it used illegal software to manipulate emissions tests on diesel vehicles in the U.S., sparking the biggest business crisis in its history. The automaker's share price has tumbled, and the scandal forced out its long-time chief executive. It also sparked investigations and lawsuits across the world.

The diesel emissions scandal affects around 11 million vehicles worldwide and was followed by an admission on carbon dioxide emission levels. The group has been forced to take extensive measures to save its reputation and shore up balance sheets.

In December, the embattled German carmaker announced a 1 billion euro ($1.07 billion) reduction in its annual capital expenditure. It also stated it would focus more on the next generation of driving technology, as well taking measures to repair its global image.

The U.S. Justice Department also sued Volkswagen for up to $46 billion for allegedly violating environmental laws in January. But Mueller said the firm may also face more than the potential $46 billion.