The statement was contained in documents filed by RBS with the Securities and Exchange Commission (SEC) to launch the stock market listing of the bank, which it hopes to sell in stages by the end of 2016.
The prospectus for Citizens stated: "The RBS Group may face the risk of full nationalisation or other resolution procedures under the Banking Act 2009, as amended by the UK Financial Services (Banking Reform) Act 2013, which could impact the RBS Group's contractual arrangements with us or result in other material effects on us."
The Government has sold down to 24.9 per cent its original 39 per cent stake in Lloyds Banking Group, owner of Bank of Scotland, obtained after its 2008 bail-out. But it retains 81 per cent of RBS after injecting £45 billion to keep it afloat during the credit crunch. There have been worries that the taxpayer might have to step in again to improve its capital cushion.
The full sale of Citizens was announced in November by RBS chief executive Ross McEwan as part of a strategy to rebuild the Scottish bank's financial strength.
Mr McEwan said: "The divestment of Citizens is a key component of our plan to continue to strengthen RBS's capital position.
"The achievement of our capital plan will allow us to focus on the needs of customers. The filing of the Citizens S-1 is an important milestone that keeps us on track for the IPO (initial public offering) of the business in the latter part of this year."
RBS plans to launch an IPO of Citizens in the fourth quarter with an initial sale of 20 percent to 25 per cent of the bank. However, full disposal is unlikely to until the end of 2016, or 12 months later if markets are unfavourable, tying the two banks' prospects together for at least 18 months.
There had been concerns Citizens' failure in stress tests conducted by US authorities in March would derail the process.
The filing of the forms kicks off a 12-14 week period for the SEC to respond before RBS launches a formal prospectus outlining how much it is seeking to raise and the price range.
Analysts value Citizens at about £9.2bn. It is held on RBS's books at £11.6bn but a price above £7.3bn would boost its capital cushion.
The documents also show that Citizens' former executive chairman Ellen Alemany was paid $7.5 million (£4.5m) last year, including $500,000 in consultancy fees for three months after she left.