Supermarket chain Sainsbury's said Wednesday that chief executive Justin King will leave the group in July, after a decade at the helm.

"Sainsbury's today announces that Justin King has decided to step down in July 2014 after 10 years as CEO, and that Mike Coupe, currently the group commercial director, will succeed him as CEO," it said in a surprise statement to the London Stock Exchange.

King has been credited with reviving the fortunes of the supermarket and more recently helping it fight off fierce competition in the supermarket sector from discount retailers like Aldi and Lidl.

He has meanwhile waived his entitlement to a cash severance payment of up to £1.7 million ($2.8 million, 2.0 million euros) on departure.

"This was not an easy decision for me to make, and in truth it will never feel like the right time to leave a company like Sainsbury's," added King, who will stand down at its annual general meeting on July 9.

In response, Sainsbury's shares fell 1.71 percent to 350.6 pence in early afternoon deals on London's FTSE 100 index, which was down 0.13 percent at 6,564.03 points.

"Kings departure will make investors nervous as to how well his successor will defend profits especially with income strapped consumers and further competition from discount supermarkets," said Spreadex analyst Lee Mumford.