The expert has already authored a report for the government into the failure of banks leading up to the financial crisis and will now consider the work carried out by the Financial Services Authority (FSA) to see what the next step is going to be, the Daily Telegraph reports.
He, along with an as-yet unnamed lawyer, will look at the results of an investigation by the FSA that has lasted almost 19 months.
According to a source familiar with the report, it is more than likely that a new investigation will be needed.
"They simply don't have the evidence to answer the question of why RBS failed and I think they will need at least another four to five months," the insider explained.
Last month, RBS predicted that its investors and clients could face increased costs following proposals by the Independent Commission on Banking that suggested retail banks may require fire breaks.
By Asim Shah