The allegation is one of the main planks of the club's case that its former chairman is the man now threatening its future.
His successor, Peter Ridsdale, makes the claim in a witness statement in which he tells how Mr Hammam said he had loaned the club £30m and that "he stood by it".
The Echo has seen the statement in a legal document laid before the court which is considering whether to order the Bluebirds to repay more than £30m immediately to Langston.
If the club loses, chairman Peter Ridsdale has said City will almost certainly go into administration.
After two days of legal argument, Judge Michael Briggs yesterday retired to consider his verdict and said he aimed to deliver it before Wednesday next week.
In outline submissions handed in to the court, Cardiff City's barrister David Wolfson lists the club's evidence for claiming "Mr Hammam equals Langston":
n Mr Hammam told Mr Ridsdale he had put £30m into the club and that he "stood behind it".
n Mr Hammam conducted all the commercial negotiations on behalf of Langston.
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