JP Morgan Chase, the only bidder for RBS' 51 per cent stake, has ruled out the purchase after Obama's announcement. But it is still keen to buy RBS Sempra's international operations which make up almost half of its overall business.
RBS is negotiating to sell the international operations to JP Morgan. Its partner, Sempra Energy, is expected to buy out the rest.
Obama's proposal, known as the Volcker Rule, was announced after JP Morgan had secured exclusivity with RBS. The rule will prevent lenders from running their own trading operations.
RBS Sempra is among the assets that RBS, which is 84 per cent-owned by the UK taxpayer, was ordered to sell so as to comply with European Union state aid rules.