BlackRock is the latest in a long line financials, companies and politicians to warn against the fiscal impact from Scotland becoming independent.
The world's biggest investment fund manager revealed in a report that Scottish independence would bring "major uncertainties, costs and risks" and that the assessment is "mostly for Scotland, but also for the remaining UK".
The Scots will be asked the straight "yes/no" question: "Should Scotland be an independent country?" on 18 September this year.
In the report, BlackRock warned against key aspects to the Scottish National Party's claims that an independent Scotland would keep the pound and its membership to the European Union, as well as remain fiscally sound on mainly oil an gas revenues.
The New York-based fund manager said that Scotland would have to launch its own currency, out of the "best of the few choices", as a currency union "looks infeasible" and would "bring risks to both countries."
It also added that Scotland's oil revenue projections were "uncertain and probably unwise" and banks, financials and insurers would face significant pressure to move headquarters to a "stronger fiscal state with a more certain regulatory backdrop".
Financials Against the 'Yes Vote'
In the run up to the referendum, a number of businesses and banks have voiced concern or plans about Scotland potentially breaking away from the UK.
Scotland's financial services accounts for about 150,000 jobs.
Alliance Trust also revealed in its latest set of results that it has started to set up a raft of England-based companies in a bid to protect itself against the possibility of Scottish independence.
Prior to Alliance Trust, insurance firm Standard Life said that it may quit its Scottish home if the nation breaks from the United Kingdom in its referendum on independence.
Britain's business secretary Vince Cable also said that it is likely that the Royal Bank of Scotland's headquarters will move to London permanently, if Scots vote for independence.