Nobody in the industry saw the move coming, admitted one wholesaler as news emerged this week that the retailer's group trading director Peter Miller had quit on 26 March.
Miller said that the "reason why I stepped down will remain forever between me and Spar".
He refused to comment on his future plans or say whether he has another position to go to.
Spar which has also refused to discuss Miller's reasons for leaving said he would not be replaced.
Miller who had a reputation as a hard negotiator and sharp trader said he was proud of the achievements he had made since taking on a role created especially for him in 2003.
These included breathing new life into Spar's own-label range, which was in decline when he joined, and forging a buying alliance with The Co-operative Group.
Spar promotional Real Deals lines, which Miller had worked closely on, had shown double-digit sales growth over the past year.
Spar's turnover increased 2.4% to £2.6bn in the year ending April 2009. "It is good to leave on a high," Miller said. "The business is in really good shape, with both sales and store numbers showing good increases."
Miller started his career at Fine Fare as a management trainee and then spent a year with Spar as an alcohol buyer.
He moved to Booker where he worked his way up to trading director and when it became part of the Big Food Group he was made group trading director before rejoining Spar in 2003.
Under a new management structure, executives who formerly reported to Miller including licensed trading director Chris Lewis, head of fresh and frozen foods Allan Maxted, and grocery trading director Mark Keeley will now report directly to MD Jerry Marwood.
One source said not replacing Miller allowed Spar to cut costs by effectively stripping out a layer of management.