The Competition Appeal Tribunal fine will be about£3.8 million higher than the£3.9 million JJB put aside for it, because of interest and higher court fees.
The sports retailer is one of seven companies being fined by the Office of Fair Trading for its role in the price fixing of England and Manchester United football shirts in 2000 and 2001.
Consumer watchdog Which? has also launched a campaign to sue the sportswear company on behalf of customers who were unlawfully charged for the replica shirts.
Which? magazine editor Malcolm Coles said: 'We hope it will soon be payback time for JJB Sports. They ripped off their customers, so we think it's only fair they should have to pay them back.'
JJB has continued to deny any involvement in illegal price fixing. The retailer said in a statement today: 'As a goodwill to our loyal customers, we will be offering a free current England away shirt to any customers who present evidence of the purchase of a 1999/2001 England home or away shirt or a Manchester United home or centenary shirt of 2000/2002.'
Evidence of purchase will include handing in one of the shirts in question to a JJB store or presenting a valid till receipt or credit-card statement.