The London stock market opened lower, with shares in supermarket Morrisons dropping more than 5% despite it reporting rising sales and profits.
The FTSE 100 index was down 42.44 points at 7,292.17 in early trade.
Morrisons was the biggest faller on the index, even though it posted a rise in underlying full-year profits for the first time in five years.
Neil Wilson at ETX Capital suggested investors thought “this could be the top of the cycle”.
“Worries about declining basket sizes, fading consumer spending health and margin pressure from a still bitter supermarket price war are weighing heavily,” he said.
However, he added: “If the latest [sales] figures from Kantar are anything to judge, Morrisons looks very well placed to cope and continue to grow sales in the face of all these headwinds.”
Shares in Aviva were having a better day, rising nearly 6% after the insurer reported a 12% rise in operating profits in 2016.
However, the company said post-tax profits dropped 22% to £859m after it took a £380m charge to cover recent changes to the way that compensation is calculated for accident victims.
In the FTSE 250, Domino’s Pizza sank 12% after the chain reported a slowdown in sales at the start of the year.
Like-for-like sales in the UK rose by 1.5% in the first nine weeks of 2017, compared with 10.5% growth a year earlier.
The news overshadowed Domino’s Pizza’s full-year results, which showed that underlying pre-tax profits had risen by 17% last year to £85.7m.