Wirecard's auditor has refused to sign off its 2019 accounts over a missing €1.9 billion.
This sent its shares down more than 60% as the German payments firm warned the delay could cause billions in loans to be called in as early as Friday.
EY was unable to confirm the existence of €1.9 billion in cash balances on trust accounts, representing around a quarter of its balance sheet, Wirecard said.
There was evidence of "spurious balance confirmations", the company added.
Wirecard's chief executive Markus Braun said that the company, which was founded in 1999, was urgently seeking to clarify the balances in question.
"It is currently unclear whether fraudulent transactions to the detriment of Wirecard have occurred. Wirecard will file a complaint against unknown persons," Braun said.
Wirecard also warned that a failure to provide certified annual and consolidated statements by Friday would allow approximately €2 billion in loans to be terminated.
In-house auditor EY had regularly approved Wirecard's accounts in recent years, and its refusal to sign off for 2019 confirms failings found in an external probe by KPMG in April.
The latest development is a stark reversal of fortune for the Munich-based fintech, which was heralded as a homegrown tech success and propelled into Germany's blue-chip DAX index in 2018 at the expense of Commerzbank.
Wirecard has long been a target of short sellers who have questioned its financials and "shorted" its stock, which fell by 60% in Frankfurt, wiping €8 billion off its market value.
Wirecard had already delayed its annual report after the KPMG report, which addressed allegations of fraud and false accounting in a series of Financial Times reports.
In the most serious finding, covering the years 2016-18, KPMG said it had been unable to verify the existence of €1 billion in revenue Wirecard booked through three obscure third-party acquiring partners.
Activist investors, led by British fund manager Chris Hohn, seized on the KPMG audit to demand the departure of Braun, who owns a 7% stake in Wirecard.
Hohn then filed a criminal complaint with the Munich prosecutor.
German financial watchdog Bafin, which previously suspected short sellers of colluding to manipulate Wirecard's share price, has shifted its attention to the company.
Prosecutors raided Wirecard's headquarters in a Munich suburb on June 5 and opened proceedings against management as part of the probe initiated by Bafin.
A spokesperson said it would investigate the latest delay to results.
Wirecard has said it was cooperating with the investigation and the allegations against it were unfounded.