The owner of Patisserie Valerie has said the cafe chain needs "an immediate injection of capital" to continue trading in its current form.
The stark statement to investors comes after the firm uncovered "significant, and potentially fraudulent, accounting irregularities".
It also belatedly discovered HMRC filed a winding-up petition against one of its principal subsidiaries in September and is seeking £1.14m in taxes.
The firm has more than 2,500 staff.
The company announced earlier this week that finance director Chris Marsh had been suspended.
Staff told the BBC that they have not been told anything by the company at all, and even the store managers are in the dark.
"I suppose it's because there's nothing wrong, but will we get paid our next month's salary in three weeks' time?" said an employee, who asked not to be named.
A long-term employee, who has worked for the company under both its current owner Risk Capital Partners and the previous owners, the Scalzo family, told the BBC that she only found out about Patisserie Valerie's problems through media coverage.
"No one has told us anything. I asked my manager and they don't know anything either," she said.
- It has five brands: Patisserie Valerie, Druckers - Vienna Patisserie, Philpotts, Baker & Spice and Flour Power City.
- Now, there are 206 stores across the chain and more than 2,500 staff as of May 2018.
- It was floated on the AIM stock market, for smaller companies, in 2014.
- The first Patisserie Valerie café was opened on Frith Street in London's Soho district in 1926.
- In 1987 the Scalzo family bought the Old Compton Street store and ran the business.
- In 2006, Luke Johnson's Risk Capital Partners bought a majority stake when it had eight stores.
In its statement on Thursday, the firm said that over the past 24 hours it had "undertaken further investigation into the financial status of the company".
The board found "a material shortfall between the reported financial status and the current financial status of the business".
"Without an immediate injection of capital, the directors are of the view that there is no scope for the business to continue trading in its current form," it continued.
The company said its "professional advisers are assessing all options available to the business to keep it trading and will update the market in due course".
Simon Jack, business editor
The news that Patisserie Valerie - a business worth £440m on Monday - is no longer a going concern without a capital injection is absolutely jaw-dropping.
The stores stay open for now. But with no cash, that cannot last, as suppliers will simply stop delivering.
The future of the company, its 206 stores and its 2,500 employees is very much in the balance.
In its most recent results statement in May, the firm said it had cash reserves of £28.8m.
Shares in the company, which is 37%-owned by entrepreneur Luke Johnson, were suspended before trading on Wednesday.
Also on Wednesday the firm announced that its board had become aware of an HMRC winding-up petition against its principal subsidiary Stonebeach, with the tax body seeking a payment of £1.14m.
One of the Stonebeach directors is Patisserie Valerie's suspended finance director Chris Marsh, according to documents filed with Companies House.
Luke Johnson, who invested in Patisserie Valerie in 2006, is a serial entrepreneur who is best known for taking control of Pizza Express in 1993 before selling out in 1999.
In 2001 he co-founded Risk Capital Partners, which owns stakes in companies including Majestic Bingo and swimming goods firm Zoggs.