Jurrien Timber said Arsenal must keep their feet on the ground after they secured a seventh consecutive victory and extended their lead at the top of the Premier League.
The London-headquartered lender will put by the provision in third quarter results due to be published on Tuesday.
David Lammy will set out a series of measures aimed at strengthening the system as he faces questions about the blunder from MPs.
It came as the Competition and Markets Authority (CMA) concluded an initial phase one investigation into the £1.2 billion deal.