Investec has maintained its 'sell' rating for UK lender Royal Bank of Scotland (RBS), recommending investors not to own the stock ahead of its third-quarter results on November 1st.Analyst Ian Gordon said that the bank will likely fall back into the red in the second half, though most of the damage will come in the fourth quarter.The 17% fall in first-half 'core' pre-tax profit to £2.5bn was entirely due to a sharply lower contribution from the Markets Division. Gordon said: "We anticipate no relief here in Q3 2013e where we expect the division to barely achieve break-even, and our expectation of slightly lower incremental losses in Ulster Bank, coupled with a modest recovery in UK Retail (reflecting both volume and margin recovery) is insufficient to offset this."The analyst added that the stock's valuation - trading at a small premium to Barclays (rated 'buy') - "appears well ahead of events" given that the target for return on equity (RoE) to be above cost of equity (CoE) won't be reached until at least 2017."Consensus continues to drift down, but we think it remains unreasonably high," Gordon said. He added that he doesn't understand how the Bloomberg consensus estimate for a RoE in 2013 is 2.17%, given that his own forecast is 0%.Gordon reiterated his 345p target price for the stock. The stock was trading down 1.38% at 371.7p on Friday morning."Despite all the considerable 'balance sheet repair', we still believe that RBS has a dangerous cocktail of legal, political and regulatory obstacles to overcome," he added.BC