Class-action suits require a volume of people to bring a case to court. The 55 number was alleged by insurance company Zurich American, a branch of Zurich Financial Services, during a separate court case against Sony, Reuters reports.
Zurich American, one of Sony's insurers, argued that its policy didn't cover damage from cyber attacks. Zurich declared its insurance was for "bodily injury, property damage or personal and advertising injury" only.
Sony bears responsibility for the fraudulent misuse of credit card details stolen from PlayStation Network account holders in the US. Things are different in the UK, where that responsibility lies with credit card companies or vendors.
This year's PSN breach saw the data of 77 million PlayStation Network accounts compromised, with the details of around 12.3 million credit cards said to be within this.
Sony expects the PSN breach to cost it £105 million by the time its fiscal year ends in March 2012.