Winterkorn was already in the sights of investigators looking at whether he failed to inform investors promptly about Volkswagen's emissions cheating scandal.
But the newspaper reported Sunday that the former VW boss may face further legal woes.
Citing investigation documents, the newspaper said Winterkorn transferred around 10 million euros to Swiss bank accounts over 2016 and 2017. Part of the sum may have incurred unpaid taxes, it added.
The claim was rejected by Winterkorn's lawyer Felix Dörr, who told Bild am Sonntag it was Winterkorn's “personal decision how and by whom he wants his assets to be managed.”
He added that the procedure was “free from any tax claim”.
According to the report, Winterkorn had transferred huge sums to his tax advisor's account. From there, the funds were sent on to Swiss accounts, including one held by Winterkorn's wife.
Prosecutors suspect that Winterkorn may be building a stash in Switzerland in case he is found liable for damages to Volkswagen over the pollution cheating scandal, said the report.
Volkswagen slumped to its biggest crisis admitting in 2015 to installing so-called “defeat devices” in 11 million diesel vehicles worldwide to cheat lab pollution tests.
Since then, several executives at the auto giant have been caught in legal trouble.
Prosecutors were already investigating Winterkorn over suspicion he may have known about the cheating earlier than he has admitted — meaning he could have failed in his duty to inform investors about the financial risks.