Singapore Post shares fell sharply yesterday after the surprise decision by chairman-designate Low Teck Seng to decline the post.
Professor Low said in a statement that he opted not to take up the role after taking time to reflect on his "principal commitment" to the National Research Foundation (NRF) as its chief executive.
The shock move sent SingPost shares down 5.5 cents, or 3.39 per cent, to close at $1.57, with 25.4 million units changing hands.
Prof Low had been named the successor to outgoing chairman Lim Ho Kee last Friday.
Mr Lim had notified the board that day of his desire to step down as chairman on May 10, when SingPost's full-year results are expected to be announced. He will also leave the board on July 14, the planned date of SingPost's annual general meeting.
In response to queries from The Straits Times, Prof Low said he had not received clearance from the NRF to take up the post of SingPost chairman when he accepted the nomination, but he added that the decision to reject it was his alone.
"Over the weekend, I decided, hey, if I am going to do myself justice and put in time for SingPost as board chairman, I won't fulfil my duties to NRF, given the stakes," said Prof Low.
The NRF chief controls a $19 billion budget from the Government to fund research, innovation and enterprise activities here over the next five years. Prof Low said he notified SingPost of his reconsideration on Tuesday and officially declined the offer on Wednesday.
"I was caught in a bit of a dilemma," Prof Low said of last Friday's SingPost board meeting.
"(After accepting Mr Lim's notice), all of us felt that it would not be good to announce him stepping down without a name to take the helm... I was proposed and the board voted unanimously. As I was the member proposed, I did not vote... The board members were informed that I would need clearance, but this was done with a view that it would be the best for SingPost."
Separately, Mr Lim acknowledged that the timing of his departure may not be ideal as SingPost is slated to deal with an audit report into the firm's corporate governance processes this month.
"There is never a perfect time for this type of transition," Mr Lim told The Straits Times.
"My original intentions would have seen me stepping down in the middle of our transformation. Having seen through the conclusion of the last financial year gives me a sense of closure and made it an appropriate time to signal I will be passing on the baton."