World-famous professional poker player Phil Ivey is suing a British casino for nearly $12 million in withheld earnings.

Ivey, 37, a fixture on the international gambling scene, won £7.6 million, or $11.9 million, in August while playing punto banco, a version of baccarat. However, Crocksfords, a casino in London, has refused to pay the winnings, alleging that Ivey used his knowledge of tiny flaws in the game’s cards to flout the game’s odds, Yahoo Sports reports.

In punto banco, each player draws two or three cards in an attempt to achieve a sum total closer to nine than the dealer. In a normal situation, the game is designed to be completely unpredictable, entirely contingent on the “luck of the draw.”

During the game, Ivey and an unidentified woman were playing “heads-up” against the dealer.  Ivey started his bets at £50,000 ($77,000) per hand, ultimately raising the stakes as high as £150,000 ($230,000). At one point during the three-night gambling spree, Ivey fell as far as £500,000 ($770,000) into the red, before rallying to achieve his $12 million in winnings.

Crocksfords said it believes that Ivey was able to spot tiny imperfections in the game’s cards, using knowledge to identify when cards of a certain value were in play, Yahoo Sports reports. The Daily Mail created an illustration of how the alleged con may have occurred.

Playing cards are designed to be marked identically, to prevent this sort of action. In addition, casinos usually replace playing cards at the end of each night, though Ivey was able to convince the casino to use the same set of cards throughout his three-day run, Yahoo Sports reports. If the cards were indeed marked by defects, Ivey could conceivably have turned that knowledge to his advantage.

Ivey maintains his right to the nearly $12 million in winnings. Crocksfords has refused to pay out, only agreeing to return the poker star’s initial £1 million “buy-in.”

"I was given a receipt for my winnings, but Crockfords has withheld payment," Ivey said in a statement. "I have no alternative but to take legal action."

Ivey, who has won nine World Series of Poker bracelets during his career, enjoys a spotless reputation among card players. Gambling pundit Lance Bradley, of Bluff magazine, described Ivey’s reputation to ABC News last fall.

"There's nothing in his past that would hint at his being a cheater or unethical in any way," Bradley said. "People say he's arguably the best poker player in the world; but, really, there's no argument: He's number one. He's known both for his skill and for his love of high-stakes games. He loves anything where there's some sexiness at stake."

Still, Crocksfords isn’t backing down. The Mayfair, London casino has enlisted fraud prevention specialists to study the tapes that captured Ivey’s wild night.