Perhaps it was the relatively cautious statement given by chief executive Dave Lewis, or the fact that while profits were above consensus expectations, sales missed by a touch.
Or maybe it's the fear that the fundamental issues plaguing the sector - ie the price wars brought about by challengers such as Aldi and Lidl aren't going anywhere.
13 April 2016 @ 9:00amTesco (TSCO)
And the UK's biggest retailer appears to be having an impact on rival grocers' share prices too.
Sainsbury's was down 1.1 per cent, while Morrisons was down 1.5 per cent.
13 April 2016 @ 9:00amMorrison (Wm) Supermarkets (MRW)
13 April 2016 @ 9:00amSainsbury (J) (SBRY)
But not everyone was struggling. Delivery group Ocado's share price was up 1.4 per cent.