Chairman of HSBC Douglas Flint has said that the bank faces a "very broad range of uncertainties and challenges" including geopolitical tensions and "eurozone membership uncertainties" - with debt-laden Greece facing a possible exit.
He also cited uncertainty of Britain's future in the EU, adding that its own research indicated that working towards reforms in Europe would be "far less risky than going it alone, given the importance of EU markets to British trade".
Mr Flint also pointed to positive trends in China, with the reshaping of its economy and further liberalisation of its currency, as well as the strength of the US.
Shares rose 3% on the announcement of the headquarters review.
More top news
The Democratic presidential candidate may also have shown his cards on his choice of running mate.
The US president also shared a post on Twitter accusing Dr Anthony Fauci of misleading the public over hydroxychloroquine.
Fears over an impending second wave of coronavirus dominates Wednesday’s front pages.