All financial statements are prepared on the going-concern basis, because assets are worth far less in liquidation. When management or the auditor concludes there is substantial doubt, that must be disclosed explicitly in the filing.
The disclosure usually follows a covenant breach, a failed refinancing or persistent losses against thin liquidity. It is rarely a surprise to anyone reading the cash-flow-statement, but it is often a surprise to the share price.
Example: a small Northwind supplier discloses substantial doubt after failing to refinance a $40M facility due in four months with $6M of cash and negative operating cash flow.
Related: auditor-opinion, covenant, refinancing-risk, contingent-liability, risk-factors