Senior insiders say the bank is preparing to make significant new provisions for compensating customers who were mis-sold interest rate swaps and payment protection insurance (PPI) policies.
Barclays is also ultimately likely to have to set aside money for potential Libor-related litigation following its £290m in fines last summer for manipulating the interbank borrowing rate.
Barclays will confirm one or more of the new provisions on Tuesday morning, according to people close to the bank.
Assuming it does make an announcement on Tuesday, it would come just a week before the bank's new chief executive, Antony Jenkins, unveils a blueprint for rebuilding Barclays' reputation.
Mr Jenkins and Sir David Walker, Barclays' chairman, will appear before the Parliamentary Commission on Banking Standards on Tuesday morning.
A person close to the bank confirmed that the sums would be "material" but declined to comment on the precise numbers involved.
Barclays has already set aside £2bn for PPI mis-selling and £450m for interest rate hedging products, the latter of which is the largest bill for any UK bank.
On Sunday, the bank confirmed Sky News' revelation that its group finance director, Chris Lucas, is to step down. Mr Lucas is one of four men under investigation by the Financial Services Authority in relation to disclosures made by Barclays during capital-raisings in 2008 that enabled it to avoid taking money from British taxpayers.
Barclays refused to comment on Monday night.