The UK's second biggest bank confirmed it was considering plans to ask shareholders for billions of pounds in extra funding.
Royal Bank of Scotland told the stock market that it was "considering a rights issue" and would make a further announcement "in due course".
The bank - which could ask shareholders for as much as £12 billion - is looking to strengthen a balance sheet weakened by losses from the credit crunch and its acquisition of Dutch rival ABN Amro last year.
It is expected to give more details of its plans to investors on Tuesday.
RBS is set to be the first in a succession of major banks to call on shareholders for extra cash as the credit crunch bites.
But chief executive Sir Fred Goodwin will also come under pressure from investors asked to stump up the money following the expected move at its annual meeting in Edinburgh on Wednesday.
The rights issue would see existing shareholders at the group offered new shares at a possible discount price. Although it would help raise billions of pounds of capital, shareholders may demand that Sir Fred steps down in return for their financial injection.
RBS could also raise billions through the sale of train leasing business Angel Trains as well as insurance companies First Direct and Churchill, according to weekend reports.
Churchill was bought from Credit Suisse in 2003 for £1.1 billion, while Direct Line could be worth around £4 billion.
The bank may also unveil around £5 billion extra in losses on mortgage-backed investments hit by the crunch - on top of the £2.5 billion write-down already taken at the group's annual results, which showed profits of more than £10 billion in 2007.
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