Former Socceroos skipper Lucas Neill has been declared bankrupt in Britain, with an investigation called.

Neill, 38, is thought to have earned about $40 million during his career. He was declared bankrupt in January.

Dale Hernon, the head of creditor services at Begbies Traynor, an insolvency firm in London, said Neill was due to be interviewed in the coming weeks, News Corp reported.

"Mr Neill is due to be interviewed when he returns to the UK in the coming weeks, at which point the trustees will be able to obtain the background information required to determine the full scale of Mr Neill's debts," Mr Hernon said.