The Sunday Times reported that the lender will now put off its marketing activities until the beginning of next year.
Under rules set out by the regulator after RBS' £45bn taxpayer bailout in 2008, it was instructed to separate off the 300-odd former Williams & Glyn branches, which it absorbed in the 1980s.
But the path of the spin-off has so far not run particularly smoothly: although the rules state it must be completed by the end of 2017, the bank admitted in April there was a "significant risk" it won't make the deadline.
This could be down to technical problems: RBS is reportedly so concerned about the challenges of creating a new technology platform for Williams & Glyn, it has even mulled selling off its Natwest subsidiary to make the transition easier.
But the decision to push back marketing may also fuel speculation RBS is considering selling the brand, rather than spinning it off. A source told City A.M. there are "people in the market" interested in buying the brand, which has 1.8m customers, including 200,000 business customers, and £24bn of deposits.
Although Santander's name has been mentioned, a previous attempt by it to buy the company ended in tears, with the Spanish lender pulling out of the deal, dubbed "Project Rainbow", in 2012.
RBS shares put in a stonking performance this morning, rising eight per cent to 239.9p in late morning trading. Although that was also to do with optimistic-looking EU referendum polls.
RBS did not comment.