The bank said Thursday that bad loans in its credit card and corporate lending businesses may increase amid "anticipated economic uncertainty in the U.K."
Britain is scheduled to leave the EU on March 29, ending more than 40 years of free trade with the bloc.
The comments came as Barclays said recent restructuring efforts delivered "improved performance across the group" last year.
Barclays says fourth-quarter pretax profit jumped to 374 million pounds from 93 million pounds a year earlier as it cut costs and set aside less money to cover past misdeeds.
The bank's net loss shrank to 76 million pounds from 1.29 billion pounds.