The federal trial of the once prominent Long Island restaurateur Harendra Singh, which was scheduled for jury selection Monday, has been delayed indefinitely, according to court records, the judge’s clerk, and sources.

Singh has been negotiating a plea deal to be a key witness in Eastern District prosecutors’ corruption case on Long Island against Nassau County Executive Edward Mangano, his wife Linda, and recently resigned Oyster Bay Town Supervisor John Venditto, according to sources.

In addition, Singh has been negotiating a similar deal with Southern District prosecutors in Manhattan probing the possible granting of favors by city officials to campaign fundraisers such as Singh.

Singh has been charged with bribery, income-tax evasion and obstruction of justice. He has pleaded not guilty in the Eastern District and has not been charged with any crimes in the Southern District.

The Manganos and Venditto also have pleaded not guilty.

It would not be unusual for a key government witnesses charged in one case to have their own trial delayed until the completion of their testimony in another case. Such witnesses are often required to secretly plead guilty so that when they testify, jurors know they will be held accountable for their crime.

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The Singh trial date was set before the Manganos and Venditto were arrested in October on charges of receiving “bribes and kickbacks” from a person identified only as a co-conspirator, but whom sources identified as Singh.

Singh’s attorney Anthony La Pinta, of Hauppauge, declined to comment on the reason for the delay in the case.

Attorneys for the Manganos, and Venditto’s attorney, also declined to comment, as did spokespersons for prosecutors in the Eastern and Southern Districts.

Singh was arrested in September 2015 on charges of bribing a former deputy Oyster Bay town attorney with $50,000 in order to help him get an ‘indirect” guarantee from the town on $32 million in loans. He was also charged with defrauding the Internal Revenue Service by failing to report millions of dollars in wages paid off-the-book, as well as cash paid by his restaurants’ customers.

In addition, Singh was charged with obstruction of justice for lying to FBI agents, and also illegally collecting $950,000 from FEMA for falsely reporting damage by superstorm Sandy to his Water’s Edge restaurant in Long Island City.

In June, U.S. District Judge Sandra Feuerstein in Central Islip set jury selection for Singh’s case to begin Monday with the trial to start immediately afterward. Feuerstein’s deputy confirmed Wednesday that the Singh case was no longer on her court calendar for that date and no future dates had been scheduled.

Federal prosecutors claimed that Linda Mangano received more than $450,000 for no-show jobs including that of a “food taster.” And Eastern District U.S. Attorney Rob Capers said that Mangano was charged with extortion for pressuring the co-conspirator to award the no-show job to his wife.

In return, the co-conspirator got hundreds of thousands of dollars in county contracts to provide food services and received multimillion dollar loan guarantees, prosecutors charged.

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In the Southern District case, prosecutors are investigating whether businessmen such as Singh, who gave tens of thousands of dollars to political campaigns, received favorable treatment in dealings with the city, according to sources. The focus of Singh’s role has been whether he received favorable treatment in the handling of the city lease on his now shut Water’s Edge restaurant in Long Island City.

DeBlasio administration officials have denied that they had engaged in any such pay-to-play scheme.