The company said he was recuperating well and expected to make a full recovery.
He will be replaced as group chief executive by Mike Morgan on a permanent basis, subject to regulatory approval.
Mr Morgan, group finance director for the last five years, assumed Mr Sainsbury’s primary responsibilities when he took his leave of absence.
Mike Biggs, chairman of Close Brothers, said: "The board would like to sincerely thank Adrian for his material contribution during his 11 years with the group, the last four of which were as chief executive.
“During this time he has overseen a period of significant growth and development, leading the organisation through a challenging period which includes covid and heightened geopolitical uncertainty."
Adrian Sainsbury said: "It has been a privilege to lead the group as chief executive for the last four years. During my time at Close Brothers I have been deeply impressed by the enduring strength of our business model, and the dedication and expertise of our people."
Mr Sainsbury was appointed group chief executive in 2020, having previously been managing director of Close Brothers’ banking division since 2016 and a director at the bank since 2013.
The company is currently embroiled in a legal battle over compensation for motor insurance finance customers.
In October the Court of Appeal published a judgment which upheld the motor commission appeals brought against Close Brothers Limited and FirstRand Bank Limited. The group has appealed the Court's decision to the Supreme Court.
The company resumed motor finance business after a temporary pause.
Close Brothers Group also owns investment and advice firm Close Brothers Asset Management, that provides advice, investment management, and self-directed services to private clients and professional advisers.
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