Michael Klein, the former head of investment banking at Citigroup who was considered Vikram Pandit’s closest rival to take on the chief executive post, is leaving the bank to “pursue other opportunities”. Klein was widely expected to leave after Pandit altered his responsibilities in March and is the most senior departure since Pandit took over.

Klein, a 23-year veteran of Citigroup and preferred choice of Sandy Weill, Citigroup’s former chief executive, to run the US bank ahead of Pandit, said in an internal memo to staff today that he was standing down as chairman of the bank’s institutional clients group, a job which he was handed in March.