Britain's Treasury and UK Financial Investments (UKFI), which manages taxpayers' 72 percent stake in the bank, have been informed that RBS directors will discuss the move at a board meeting this week, Sky reported, citing unidentified sources.
Sky said the precise size of the provision, to be included in the bank's 2016 full-year results, was unclear, though it cited another source as saying it could be between $3 billion and $4 billion.
A formal statement about the charge could come as soon as Thursday, Sky added.
RBS and the Treasury declined to comment. UKFI could not immediately be reached for comment.
RBS is in the middle of a restructuring, which includes asset sales, job cuts and multi-billion dollar charges to settle litigation and pay regulatory fines for past misconduct.
The bank concluded agreements to sell at least $600 million worth of shipping loans from its portfolio as part of efforts to exit the sector, sources with direct knowledge of the deal told Reuters on Friday.
(Reporting by Ismail Shakil in Bengaluru and Lawrence White in London; Editing by Mark Potter)
