The London Olympic games in 2012 should bring economic benefits to UK firms, but many are not sufficiently prepared to take advantage, a report says.
At the same time many companies are not aware of the potential risk of disruption from the event, says the survey from Deloitte.
The report comes in the week that the Commonwealth Games have ended, and eyes turn to London in two years' time.
"Many of these businesses need a wake-up call," says Deloitte.
"We believe that - with insight and planning - businesses can maximise the opportunities to benefit commercially from London 2012," added Rick Cudworth, head of business continuity and resilience at Deloitte.
"The clock is ticking and the planning needs to start now."
The report from the international auditing and business consulting firm also says that 60% of businesses in London expect virtually no impact on their ability to operate "business as usual" during the games.
Meanwhile, 70% of UK retailers expect no impact, despite this industry being one Deloitte feels "faces a direct impact in terms of a need to have high numbers of staff in store and product on the shelf".
Transport is a worry for firms but the report says very few are concerned about supply disruption or resource scarcity, such as hotel rooms - which Deloitte says will be in short supply.
More than half of companies surveyed expect the Games to deliver an increase in demand for their services.
But, said Deloitte, even here "there is a disconnect with many companies expecting an increase in demand, but not planning for how they are going to secure that extra business".
However, it also says that many businesses have recognised the need to plan for the games.
About a quarter of large businesses in the UK have appointed an individual or group to manage the potential risks to their business and assess the opportunities on offer as a result of the Games.
Heather Hancock, London 2012 Partner at Deloitte, said: "It's a good start that, with just under two years to go, 25% of the businesses we surveyed are already thinking about the impact and the opportunities of London 2012.
"These companies stand to be best-placed to benefit from the business boost the Games can deliver."