It comes after chairman Stephen Green announced he was leaving earlier than expected to become a trade minister.
The BBC understands finance director Doug Flint will replace him, if city regulator the FSA gives its approval.
Meanwhile another front-runner for the post, chief executive Mike Geoghegan, is understood to have resigned.
Stuart Gulliver, who runs HSBC’s investment bank, is expected to replace him, BBC business editor Robert Peston said.
A bank spokesman declined to comment on speculation, adding that the hunt for a new chairman was ongoing.
The Financial Services Authority is yet to approve either appointment, the BBC understands – although if clearance is given, an official announcement is likely on Friday.
HSBC has a history of promoting its chief executive to the chairmanship and Mr Geoghegan had been seen as a front-runner for the position.
The bank denied reports that he was to quit after being told he was being overlooked for the position.
But our business editor said news of the departure at the same time as Mr Flint’s appointment meant the bank would “find it hard to dispel the impression that Mr Geoghegan is disappointed at being leapfrogged”.
“The saga of the replacement of Stephen Green as chairman of HSBC is turning into a farce, which is delicious for spectators but humiliating for one of the world’s most proper and secretive banks,” our business editor added.
“For all HSBC’s success in steering a pretty steady course through the worst banking crisis in 60 years, some would argue that succession planning at such a vast and powerful organisation ought to be a little more orderly.”
Mr Green will take up the position of minister for trade and industry from January, ending his 28-year career at HSBC, having spent three years as chief executive and four years as chairman.
At the time of the appointment, HSBC said the move was in response to a request from the prime minister.
This week the chief executive of the Lloyds Banking Group, Eric Daniels, said he was to retire in a year’s time.
And earlier this month one of the world’s highest paid bankers, Bob Diamond, was to become chief executive of Barclays – replacing current chief executive John Varley next year. – BBC