Kirill Rapoport pleaded guilty in August to running poker games in Manhattan. He’s one of more than 30 people charged in connection with a $100 million gambling operation tied to Russian mobsters. The feds contend he used threats of violence — and on at least one occasion mixed martial arts goons — to scare losers into paying up.

Pay up — or step inside the cage.

A Brooklyn tough guy brought two menacing mixed martial arts fighters with him to collect a debt from a poker player, according to federal prosecutors who asked a judge to give the crook at least six months in jail.

Kirill Rapoport, 41, one of more than 30 people charged in April in connection with a $100 million gambling operation tied to Russian mobsters, pleaded guilty in August to running poker games in Manhattan.

The feds contend he acted as a “collector” who used threats of violence — and on at least one occasion MMA goons — to scare losers into paying up. He worked alongside Arthur Azen, 44, of Staten Island, who pleaded guilty last month to money laundering conspiracy and extortionate credit collection.

“On Oct. 5, 2012, Federal Bureau of Investigation agents observed the defendant, Azen and two mixed martial arts fighters go to meet with a player in Azen’s poker games, who based on earlier interceptions appeared to be delinquent in playing Azen’s debts,” prosecutors wrote Sunday in a presentence letter to Manhattan Federal Judge Jesse Furman.

“Out of concern that Rapoport, Azen and the MMA fighters might physically harm the player and in order not to reveal the ongoing FBI investigation, the FBI arranged for the New York City Police Department to intervene in the meeting by claiming they had received a report of someone smoking marijuana in the area,” the feds added.

FBI agents later spoke to the poker player, who confirmed that he owed Azen $35,000 to $40,000 in poker debts.

Rapoport faces up to five years in prison and is scheduled to be sentenced Thursday. His plea deal calls for six to 12 months behind bars.

“The defendant’s role in the offense was serious. He was not a dealer or a bartender,” prosecutors said in the presentencing letter. “His job was to make sure that bettors at Azen’s illegal poker games and bettors of Azen’s sports book paid their debts.”

Prosecutors said Rapoport was a relatively small cog in an operation that catered to wealthy gamblers and celebrities.

His lawyer Jay Schwitzman told reporters in August that what Rapoport did was “hardly different from what you and I do when we play poker.” Schwitzman also said the feds targeted Rapoport because of his Russian background.

“They targeted him because of his ethnicity … He was not part of any Russian mob,” Schwitzman said.

But when Rapoport was arrested April 16, he had brass knuckles in his dresser and an inoperable gun in his apartment, prosecutors said in their letter.

“These weapons are the tools of the trade for an ‘enforcer’ who threatens the use of force to collect debts,” they wrote.

The feds declined to provide details on the so-called MMA fighters Monday, and Schwitzman declined to comment.

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