The accounting watchdog is investigating KPMG over its last audit of collapsed Bargain Booze owner Conviviality.
The Financial Reporting Council (FRC) said the probe related to its work on Conviviality's final set of full-year results before the firm fell into administration, covering the 52 weeks to April 30 2017.
It is also carrying out an inquiry under the Accountancy Scheme over the preparation and approval of Conviviality's financial statements and other financial information by a member of the Institute of Chartered Accountants in England and Wales (ICAEW).
The Accountancy Scheme provides a system for investigating members of the accountancy profession over their conduct, and provides guidelines for disciplinary proceedings if necessary.
The FRC did not disclose the name of the ICAEW member facing scrutiny.
Conviviality fell into administration on April 5, after a string of profit warnings and the discovery of a £30 million tax bill, which was revealed to markets in March.
The company - which was already suffering from soft margins at the start of the year- had also found a "material error" in the forecasts for its Conviviality Direct business.
The black hole created what the company called a "short-term funding requirement" and its shares were subsequently suspended.
Conviviality was then forced to go cap-in-hand to investors to raise £125 million as a result, but was unable to convince them of its long-term future.
Its wholesale arm - which included brands Matthew Clark, Bibendum, Catalyst, Peppermint, Elastic and Walker & Wodehouse - was snapped up by C&C with support from AB InBev for a nominal sum in April.
The retail arm, which included Bargain Booze, Wine Rack, WS Retail and Select Convenience, was then bought by food wholesaler Bestway in a £7 million deal.
The audit probe is the latest to hit KPMG, which last month was slapped with a £4.5 million fine by the FRC over its audit of insurance firm Quindell.
Quindell, now renamed Watchstone, was rocked by a series of scandals in 2015 and was also investigated by the Serious Fraud Office.
It comes as the wider accountancy sector suffers a reputation crisis in the wake of the high-profile collapse of Carillion.
A damning parliamentary report released last month called on the Competition and Markets Authority to examine a break-up of the Big Four following failings exposed by Carillion's administration.
The construction and outsourcing giant left behind a £900 million debt pile, a £590 million pension deficit and hundreds of millions of pounds in unfinished public contracts.
The Big Four - KPMG, PwC, Deloitte and EY - were accused by MPs of "prioritising their own profits ahead of good governance at the companies they are supposed to be putting under the microscope".