UBS reportedly plans to announce up to 10,000 job cuts worldwide as it slims down its investment banking activities.
The cuts, equivalent to up to 16% of its 63,000 workforce, have been reported by both the Financial Times and the Reuters news agency, each citing anonymous sources.
The Swiss bank's large debt trading business is to be split off into a separate unit that will be wound down over time, according to the FT report.
UBS declined to comment on the reports.
The bank's UK workforce numbers 6,500, and London is also the main centre for the trading and sales activities of its investment banking operations, which are said to be hardest hit by the cuts.
UBS has made clear in the past that it plans to shift its focus away from investment banking, towards its core business of looking after and advising on the investments of wealthy individuals.
The bank suffered total losses of 39bn francs (£26bn; $42bn) during the 2007-09 financial crisis, particularly due to investments in US sub prime debt, and had to be bailed out by the Swiss authorities.
Last year, UBS lost a further 2bn francs due to Kweku Adoboli, an alleged rogue trader on one of its investment bank's equity trading desks, prompting the chief executive Oswald Gruebel to resign.
Mr Adoboli is currently on trial for fraud and false accounting - charges that he denies.
The Swiss authorities have come down hard on UBS and fellow Swiss bank Credit Suisse, demanding that the two increase their loss-absorbing capital to 19% of their risk-adjusted assets, far higher than the new 10.5% hurdle that has been set internationally.
The need for UBS to increase its capital - and cut its risky investments - was among the reported reasons for the job cuts.
Investment banking is also proving to be a less profitable business line than during the heyday of the last decade, with all of the big global trading firms facing weaker revenue growth.