The company says sales dropped 52% in the 20 weeks to 13 December, or 29% on a like for like basis when the impact of store closures is left out.
December sales have plummeted further, the company says, down 32% n the first three weeks of December.
The retailer is trying to recover from a difficult year that saw suppliers hold back stock as it fought to stave off administration. The chain has struggled with debt and competition from rivals such as Sports Direct.
It reported a £42.9m loss for the first half of the year.
JJB says it does expect to receive its full stock package until early next year and consequently will “continue to be cautious about Christmas and New Year and expect that trading within the current environment will remain difficult.”