The chairman of banking giant HSBC warned on Friday that uncertainty over the economic future of Scotland could lead to "capital flight" if it votes to leave the United Kingdom next month.
Writing in British daily The Telegraph, HSBC head Douglas Flint said the currency union with England was an "anchor" for Scotland's stability and leaving it "would be complex and fraught with danger".
Flint, himself a Scot, is the most high-profile business leader to speak out against Scotland leaving the United Kingdom before the September 18 vote.
"Uncertainty over the Scotland's currency arrangements could prompt capital flight from the country, leaving its financial system in a parlous state," he wrote in the newspaper.
Currency has been a major part of the debate, with the Scottish government saying it would seek to remain part of a formal currency union even as a separate state. Westminster has ruled out such a deal.
A poll published this week found that the majority of English people oppose Scotland continuing to use the pound if it votes to become independent.
If Scotland does back independence, it could also choose to set up its own currency, attempt to join the euro or continue to use sterling without the Bank of England as lender of last resort.
"In all these circumstances, the transition from the existing currency union would be complex and fraught with danger," said Flint.
Introducing a new currency "would be an enormous challenge for an independent Scotland" and it would take "many years for the country to establish its credibility," he said.
Choosing an informal link to sterling would also place "enormous pressure" on Scotland's finances and leave it with no room to manoeuvre in times of trouble, he said.
"In all of these scenarios, Scotland's borrowing costs and those of its businesses and consumers would rise –- at least in the near term," Flint added.
Flint reportedly donated £25,000 ($41,500, 31,200 euros) to the campaign for a united Britain last year.