But he added: "This 'short squeeze', seemingly also affecting Tesco ( LON:TSCO ) this morning, shouldn't signal a full-blown sector rebound – after all, the supermarket war continues to rage in the background." Shore Capital said it was keeping its 'sell' advice on the stock. The broker's Clive Black and Darren Shirley said in a note: "Whilst we applaud the focus of Sainsbury 's management, keeping store standards tight and extolling points of difference where they are real, we believe the mix of deflation, gross margin investment and scope for market share loss‎ mean that the downgrade cycle could be reasonably deep and sustained."