The Australian Securities Exchange has made informal requests for Westpac to explain persistent market speculation that it is searching for a replacement for its chief executive, Peter King, before the end of the year.

The market operator declined to comment. But two sources with direct knowledge of the discussions between the exchange and the bank told AFR Weekend that the ASX had been in informal contact with Westpac this week about what its chairman, Steven Gregg, had told analysts and investors in recent closed-door meetings.