Nearly two-thirds of businesses fear another lockdown, while one in five is trading at a loss, a CSO survey has found.
KBC Ireland economist Austin Hughes said the figures showed that most firms have proved surprisingly resilient - but a large minority would risk collapse if a Covid-19 surge forced a second lockdown.
The survey, he said, pinpointed "fear that reflects their experience of the first lockdown. They survived that and have some capacity to work their way out of the damage from one lockdown".
"But strike two and many of them are out. A second lockdown would make their business unviable," he said.
Even firms reporting strong trade say social-distancing requirements have left them struggling to post a profit.
At the Liberty Grill in Cork, the usual outdoor queues for brunch and lunch have been replaced by an app-driven queue-management system called WalkUp. The number of tables has been cut in half to eight, and the staff reduced from 17 to 10, all paid by the Temporary Wage Subsidy Scheme (TWSS).
The diner's manager, Jason O'Sullivan, says virtually all tables are booked solid by locals and staycationers as early as 8:30am. But social distancing means sales volume is still less than half what it would be in normal times.
"If we're not full from the morning to the evening, then we won't make ends meet," he said. "With the wage subsidies we're breaking even."
The Liberty Grill is surrounded by pubs and clubs - most of them still closed. Mr O'Sullivan fears that many of these once-thriving social hubs will struggle to reopen the longer they are deprived of trade.
"Two pubs are open out of 15 to 20 pubs along Washington Street," he said. "It will get a bit grim when tourist season dies down and reality looks in. It will be a very different landscape come the spring."
Mr Hughes said the CSO's finding that 96pc of firms are currently open is positive - but masks the fact that certain sectors face an existential crisis that will require precisely targeted grants to manage.
"Half of businesses are still saying that the situation is effectively normal. But certain types of firms are struggling to keep their head above water," he said. "They will need support beyond the July stimulus."
In July, the Government unveiled new spending of €5.4bn to boost the economy.
The CSO survey was published yesterday before the Government announced a new round of restrictions.
Responses from 750 firms reveal an economy almost evenly split between those trading relatively normally and those struggling to survive.
Nearly 60pc said they have enough finance to survive at least six months. Half said they had taken no State aid since the pandemic began.
Of those seeking aid, their overwhelming choice is to take grants and avoid loans. Nearly half have staff on the TWSS, and 11pc have taken the local council-issued Restart Grant. Only 2pc have received finance via the Working Capital Loan Scheme.
When asked to identify their biggest concerns, 64pc picked 'an increase of Covid-19 cases leading to another lockdown'. Weak turnover, cashflow problems and rising costs ranked as lesser worries.