Sport Direct has warned that early 2011 "will be extremely challenging for all retailers in the UK".
It came as it said its latest half-year results would be "significantly above" a year earlier, thanks to a sales boost from the summer's World Cup.
In its trading update, the firm said its total sales in the nine weeks to 26 September were up 5.4%. It did not release a like-for-like figure.
It will release its results for the half-year to 24 October in December.
In addition to its network of stores, Sports Direct also owns sports brands including Dunlop, Slazenger and Lonsdale.
On Tuesday, the Serious Fraud Office announced that its investigation into Sports Direct and JJB Sport over an alleged cartel had been dropped with no charges brought.