One trader called Tesco's shares down by as much as 10-12 percent at the open, while another expected Tesco to fall by 5-10 percent.

"Tesco used to be the most innovative store in the grocery market but given that Aldi and Lidl have taken its customers by cutting the price of their products without compromising too much on quality, Tesco has been extremely slow to respond to those changes. Today's news is another disaster for the company," said AvaTrade chief market analyst Naeem Aslam.

(Reporting by Sudip Kar-Gupta; Editing by Atul Prakash)