Deutsche Bank is said to be considering whether to relocate some of its UK operations if Britain left the EU which could impact on its base in Birmingham.
The German bank moved hundreds of staff out of London to Brindleyplace as part of a wider change programme by the group which saw employees move to new locations across its global operations.
According to reports, Deutsche Bank has established a working group to assess the consequences of a possible departure by Britain, known as 'Brexit', following an in/out referendum which Prime Minister David Cameron has pledged to hold by 2017.
A spokesman for the bank told the BBC it was "early days and no decisions have been made".
The Financial Times said it was the first financial giant to review its position formally and it would consider whether to move some parts of the business back to Germany.
According to the company's website it employs more than 8,000 people in the UK with more than 2,000 at Five Brindleyplace including a trading floor and serving clients previously handled by teams in the captial.
The news comes after senior figures at Staffordshire manufacturing giant JCB this week suggested the UK would not suffer any adverse effects from leaving the EU.
Chairman Lord Bamford, who is also a Tory donor, backed the idea of Britain leaving the EU, telling the BBC the country could exist "peacefully and sensibly" on its own.
And JCB chief executive Graeme Macdonald told a newspaper that Britain should leave the EU unless it reformed, playing down fears that an exit could hit exports to the continent.
He told the Guardian: "I really don't think it would make a blind bit of difference to trade with Europe (if the UK left an unreformed EU).
"There has been far too much scaremongering about things like jobs. I don't think it's in anyone's interest to stop trade. I don't think we or Brussels will put up trade barriers."