Scotland would face an "enormous challenge" to produce their own currency if it became independent, according to the chair of HSBC, Douglas Flint.
He said: "Scotland would be faced with monetary policy implementation without representation - a very odd form of independence."
The three main parties at Westminster have all ruled out the Scottish Government's preferred option of a formal currency union between an independent Scotland and the rest of the UK.
The Scottish referendum vote will take place on September 18.
More top news
Wet and windy for a time across many areas through this evening
The US president is losing another of his key aides in the latest of a string of high-profile departures.
Sir Bruce entertained audiences for more than seven decades.