Outdoor clothing specialist Blacks Leisure blamed the World Cup and the lack of a Glastonbury Festival for a "disappointing" sales performance.
The group said like-for-like sales were one per cent down over the last 20 weeks, while it added that trading conditions were likely to remain challenging.
As a result, the company warned that profits for the half-year to August 31 were expected to be below last year's level, when the Millets owner achieved a figure of £6.9 million.
Blacks said the sales performance needed to be viewed in the context of the World Cup, which had a significant impact on sales in June and early July, while it also pointed to Glastonbury's absence and the continued dry weather.
The company said it expected a post-World Cup boost to business during the rest of the camping and hiking season.
"However, we now expect the profit result for the first half to be below that of last year," it added.
Shares closed down 60p at 490p.