The boss of home improvements chain B&Q has warned that investment would be put on pause in Scotland if there is a vote for independence.
Sir Ian Cheshire, whose multinational firm Kingfisher owns the DIY outlets, said there are too many uncertainties surrounding currency and Scotland's place in the EU.
The prospect of a Yes vote in September also puts on hold plans for a further 23 Screwfix shops, he said.
Sir Ian, speaking at his newest B&Q warehouse in Port Glasgow, Inverclyde, insisted he will not pull out if Scots decide to leave the union.
But he said: "It would put a pause on everything.
"If we have differences on VAT, currency, it just puts everything into hibernation as we try to figure out what it will mean.
"At the end of that we have to consider what is the trading environment.
"Because Scotland is such an important part of B&Q, there's no way we're going to let it go, but it would be more complicated, probably more costly and less likely to attract investment, given we could invest in 11 other countries around the world."
B&Q employs more than 2,600 people in Scotland and around 20,000 across the UK. Screwfix, which Kingfisher also owns, has 27 shops in Scotland employing just under 400 people.
Although Sir Ian's company operates across borders, the impact of change would cause him problems.
The company's UK-wide IT system would have to change and thousands of products may have to be repriced in B&Q and Screwfix, he said.
He insisted his warnings are from a purely business angle, and that it would be wrong to say Scotland would not be capable of being independent.
"Whatever the result of the referendum, we will be here," he said.
"In some of the early stages of the debate there were some extreme claims being thrown about on both sides.
"Some claimed Scotland couldn't possibly survive on its own as an independent state, which is clearly ridiculous - of course it can be.
"There are equally some scare stories on the other side."
But he said he would "strongly advise" a vote against independence.
"There are lots of other reasons you might believe in, historical, political reasons for independence, I totally respect that," he said.
"From a business point of view I would strongly not advise it. There's no way I can make that decision and I'm very conscious that, given the polls, a large chunk of our customers will also be voting Yes, and again I respect that.
"As a business, through our lens, it is clearly better to be part of the UK."
He would have to "wait and see" if conditions were good enough to open more stores, including plans to take the number of Screwfix outlets up to 50 in Scotland.
"Those may or may not happen as a result," he said.
He highlighted competing versions of how quickly or seamlessly Scotland might fit in to the EU as a member state.
"Technically, the UK is part of the EU and if you leave the UK you will have to reapply," he said. "I spend a lot of time in Brussels and I've been told this consistently by a large number of people.
"We see a real problem here and see a real problem with the currency because I just don't see any way in which the UK Government in Westminster is going to agree to a currency union.
"I've heard this up close and personal from both sides of the Coalition, so there has to be some sort of alternative.
"There's always a way of making things work, but the question is, basically, is this better than the current situation? I would say not. I can see the downside, I can't really see the upside."
Earlier this year, Chancellor George Osborne and other UK party leaders ruled out the Scottish Government's preferred option of creating a sterling union across the border after independence.
The Scottish Government's White Paper on independence also sets out the case for smooth transition to EU membership within the 18 months between a Yes vote and formal independence in 2016.
Sir Ian, who is not eligible to vote on September 18, discussed his views on the referendum with Scottish Labour leader Johann Lamont and local Labour MSP Duncan McNeil during his visit to Port Glasgow.
Pro-independence group Business for Scotland argues that keeping a currency union is in the best interests of the rest of the UK.
It also says the UK Government is choosing not to get clarity on potential Scottish membership of the EU because ministers know the answer would be in Scotland's favour.
And it warns that remaining in the UK could see Scotland pulled out of the EU regardless after a promised referendum on European membership.
Tony Banks, chairman of Balhousie Care Group and Business for Scotland, said: "We welcome Sir Ian's confirmation that his companies and associated jobs will remain in Scotland after a 'Yes' vote. Inward investment is of course at a record high and Scotland's economy is out-performing the rest of the UK in the lead up to the referendum.
"Sir Ian has quite rightly dismissed as ridiculous the scaremongering of the 'No' campaign that Scotland could not survive as an independent country.
"We will seek a discussion with Sir Ian to clarify some misconceptions about independence promoted by the self-styled Project Fear.
"An independent Scotland will remain in a common market and we believe there will be no change of currency. A senior UK Government minister has admitted the currency union will be continued. There will be no barriers to trade and in actual fact significant opportunities through the tax system to reduce costs for companies operating in Scotland.
"The only risk of red tape and barriers to trade comes with a 'No' vote after which it looks increasingly likely Scotland will be dragged out of Europe by the rest of the UK. Kingfisher could usefully consider re-locating its headquarters to Scotland. If and when they do, we will welcome the company, more new investment and jobs with open arms."
Scottish Labour MP Anne McGuire said the union is good for firms and good for jobs.
" Why would we want to put that at risk by putting up a barrier between employers and their customers elsewhere in the UK?" she said.
"B&Q is just the latest in a long line of large employers in Scotland who have warned about the risks and uncertainties of separation.
"Sir Ian is right to call for a plan B on currency. What we need to hear from (First Minister) Alex Salmond is what would replace the pound if we leave the UK? Would we rush to set up the euro or would we set up a separate unproven currency? The idea that the nationalists can keep this information hidden from Scots before the vote simply isn't credible.
"As part of the UK we can have the best of both worlds - our strong Scottish Parliament, with the guarantee of more powers for Scotland, backed up by the strength, security and stability of being part of the larger UK. Only separation puts that at risk."