CBA's new chief executive Matt Comyn copped another blow on Monday after the group's respected chief financial officer, Rob Jesudason, announced he had left the bank to take up a senior role with global blockchain provider, Block.one.Banking Day understands that Jesudason, who held the CFO post for less than a year, previously held ambitions to succeed Ian Narev in the top job but last year was encouraged by the board not to apply.A bank source said Comyn had been keen to retain Jesudason until the end of 2018 given that there were already five vacancies on his senior management team.The source said that Jesudason told Comyn he would stay in the role but suddenly tendered his resignation over the weekend after his appointment as an executive director of Block.one was confirmed.Investment analysts said the resignation was a setback for the group as the former CFO was viewed in the market as a "cleanskin" removed from the Austrac controversy and other debacles weighing on the bank."Rob did a great job of reaching out to the market after the Austrac matters surfaced," said CLSA bank analyst, Brian Johnson."His departure is definitely a blow to the organisation."Johnson said the resignation created another hole in the bank's depleted senior executive ranks."Six out of the twelve senior management positions are now empty," he said."This needs to be sorted out quickly."The bank has appointed Alan Docherty, an executive from its institutional division, to act as CFO until a global search to replace Jesudason is completed.Comyn's disappointment at his CFO's earlier-than-expected departure might have been reflected in the wording of the announcement filed to the ASX on Monday, which did not acknowledge Jesudason's contribution to the bank in various roles over seven years.The resignation comes at a particularly sensitive moment for CBA as Comyn and board chair Catherine Livingstone review the bank's strategic bearings following recent governance scandals.Comyn is said to be developing a simplified business model to take the bank forward that is likely to rein in activities outside the group's core retail and institutional banking operations.While some institutional investors expect Comyn to rein in parts of the Asian banking network, a strategic sale of some operations could trigger writedowns of carrying values.Banking Day recently reported that CBA has doubled the carrying value of its 18 per cent stake in China's Bank of Hangzhou since 2014, despite a sharp fall in the market value of the company's scrip on the Shanghai stock exchange.Before he was appointed CFO, Jesudason led CBA's international division, which has continued to develop several businesses he introduced to the group.One of those businesses, the South African-based TymeDigital arm, could become an important driver of Comyn's simplification program.In the last 12 months, CBA has begun to digitise its banking distribution in Indonesia where it currently has a network of 80 branches.The bank recently told Indonesian customers that they would no longer receive printed statements from 1 August under a program to migrate accounts to the Tyme digital banking platform.CBA will also terminate all