Prosecuting, Sarah Whitehouse QC told the court that in a report submitted this week, the doctor assessing Mr Cohen had asked for more time.
She told judge Richard Leon Marks QC, the Common Serjeant of London, that it is 'unclear' how much time will be needed.
The date for Mr Cohen's trial - which was set for February 5 - was deferred.
Mr Cohen, represented by John Femi-Ola QC, will next appear in court for a plea and trial preparation hearing on February 2.