Sky News understands that the bank will make provisions for compensation for customers who were mis-sold payment protection insurance (PPI), interest rate derivatives and identity theft cover through the stricken credit card insurer CPP.
Insiders said this weekend that Barclays chief executive Antony Jenkins had been told by its regulators to be "conservative" in topping up its previous £2.6bn provision for PPI and an £850m bill for mis-selling swap products - designed to insure customers against sharp interest rate movements - to small businesses.
Barclays directors are also understood to have discussed taking its first hit for compensating CPP customers at a board meeting this week.
The final bill will be signed off by Mr Jenkins, Sir David Walker, the bank's chairman, and the soon-to-depart finance director Chris Lucas on Monday.
A Barclays spokesman declined to comment on the size of the new compensation figures but it is understood that they will take the amount it has set aside for swaps mis-selling to well over £1bn.
The scale of the new provisions will partly explain why Barclays is also planning to announce a major capital-raising comprising conventional shares and contingent convertible (or 'coco') bonds alongside its results.
That follows pressure from the Prudential Regulation Authority for Barclays to meet a target measuring the strength of its balance sheet, called the leverage ratio, by the end of next year.
The announcement will be made as part of Barclays' half-year results on Tuesday, and could undermine Mr Jenkins' efforts to overhaul the bank's reputation following last summer's Libor rate-rigging scandal.
Barclays was fined £290m for its role in the affair, leading to the departure of Mr Jenkins' predecessor, Bob Diamond.
Barclays will not be the only lender to add to its PPI mis-selling provisions during next week's results, with Lloyds Banking Group (Other OTC: LLOBF - news) and others also expected to belie suggestions that the tidal wave of compensation claims had abated.
Barclays has, though, been particularly affected by the way interest is calculated on PPI compensation claims because of its liabilities dating back many years.
Mr Jenkins will also spell out the progress of his overhaul of the bank, called Transform, in which he will say that Barclays is exceeding cost-reduction targets announced in February.
Barclays declined to comment.