A gambling "addict" is fighting a High Court bid by the Ritz Club casino to recover more than £2 million.
Safa Abdulla Al-Geabury, who says he is worth more than a billion dollars, wrote a cheque for £2 million on February 19 2014, in exchange for roulette chips, but it was returned unpaid.
Now, the Ritz Hotel Casino Ltd, which markets its Ritz Club as one of the most luxurious and exclusive in the world, wants to recover the sum plus interest, which is running at £438 a day.
Mr Al-Geabury, who rents homes in Sloane Street and Chelsea in London and in Geneva, does not dispute signing the cheque but says that in November 2009, in an attempt to control his gambling disorder, he self-excluded himself for life from the Club's casino.
His counsel Kevin Pettican has told Mrs Justice Simler that by providing Mr Al-Geabury with facilities to gamble after that date, the Club unlawfully breached the terms of its gaming licence.
As well as contesting the action, Mr Al-Geabury is counter-claiming for £3.4 million - or £5.4 million in the event that the judge decides that he is liable on the cheque.
This represents the sums he lost when he was allowed to gamble between October 2010 and February 2014.
Mr Al-Geabury, 52, who put his case today through an interpreter, says that before he signed the Ritz form, he had already excluded himself from Grosvenor Casinos and Aspinalls Club.
He also excluded himself from all casinos operated by London Clubs International, writing on his form: "I have brain problem. I am addict of gambling."
His written evidence was that he managed to stay away from casinos for 10 days in February 2014 and took steps to limit his access to money by not transferring funds to his UK account.
This meant he could not gamble at the Ritz Club where he was required to purchase chips with his debit card.
But he claimed that a cheque cashing facility was put in place by the Ritz Club's chief executive officer after a conversation they had during a football match at the Emirates Stadium on February 19.
After the game, he went to the Club and was provided with the cheque which he signed before losing £2 million in chips in less than two hours.
Unable to return further credit, he demanded another self-exclusion form which he signed and then left.
The hearing in London, which is due to last five days, will hear evidence from psychiatrists about the extent of Mr Al-Geabury's disorder and whether it should have been obvious to the Club's staff.