Unnamed sources were quoted by Reuters as saying that Barclays is one of six banks in talks with UK regulators to pay nearly £1.5bn in a group settlement.
A potential agreement is likely to be finalised in mid-November and US regulators were also working on a group payment, the sources added.
Barclays Finance director Tushar Morzaria said: "These are ongoing discussions with certain regulatory agencies and it’s our best estimate of what we feel is the provision required as a consequence.
"The discussions are fluid and they are continuing."
The US and UK regulators, including the Serious Fraud Office and Financial Conduct Authority (FCA) is currently investigating allegations of attempted manipulation of the $5.3trn-a-day forex market and information sharing between traders.
Three of the other banks being investigated, UBS, JP Morgan Chase, and Deutsche Bank, have each set aside more than $1bn in the third quarter for additional legal costs.
Meanwhile, Royal Bank of Scotland and HSBC are expected to announce provisions on today and 3 November, respectively.
Barclays, which reported a rise in pre-tax profits for the first nine months of the year, also reserved further £170m to cover the cost of mis-selling payment protection insurance (PPI), which takes the total PPI bill for Barclays to more than £5bn.
However, the lender’s investment bank revenues dropped 10% in the quarter compared to previous year.
Morzaria said: "The dark pools allegations that happened right at the start of the quarter have had an impact."
Barclays paid £290m fine for manipulating the London Interbank Offered Rate (Libor) in 2012.
Image: Barclays reserved £500m to cover potential fines for foerx rigging. Photo: C Ford.
