Five-time heavyweight boxing champ Floyd Mayweather Jr. is taking a swing at an ex-con major donor to former Mayor Bill de Blasio over an alleged $175 million fraud scheme involving jewels and a secret jet sale.

The superstar pugilist claims in a new Manhattan Supreme Court lawsuit that Jona Rechnitz — an ex-mayoral donor who once tried to bribe NYPD cops with hookers — orchestrated “a multi-year fraudulent scheme” involving real estate, jewelry and his beloved Gulfstream Jet famously emblazoned with “MAYWEATHER” on the fuselage.

“As they say, the gloves are off,” Mayweather’s lawyer, Leo Jacobs, told The Post. “This case is about restoring to our client what is rightfully his.”

Rechnitz had spent years cultivating a relationship with Mayweather, who has earned a reported $1 billion during his career but whose high-flying lifestyle has left him cash-strapped at times.

In 2024, Rechnitz became the “de-facto” manager of the boxer’s investment, banking and real-estate assets — before betraying the champ’s trust by diverting his fortune to himself and a broker pal, according to legal documents. 

Rechnitz previously pled guilty in 2016 for his role in the infamous prostitute-packed NYPD corruption scandal that also involved private jets.

He had been a top donor to de Blasio — who called him a “brother” in emails.

Mayweather says in his suit that Rechnitz hid his criminal past from him, which has included a separate $17.7 million judgement against the former powerbroker and his pal Ayel Frist, who also is being sued by Mayweather.

The boxer’s lawsuit demands that Rechnitz pays back the claimed $175 million in losses — detailing exactly how the alleged jaw-dropping clandestine fraud went down.

In July 2024, Rechnitz took it upon himself to wire $7.5 million from one of Mayweather’s companies to a Florida LLC owned by his pal Frist, stating it was for an imaginary “12-month investment” that never materialized, according to the suit.

A year later, Rechnitz schemed to bring roughly $100 million of Mayweather’s jewelry to a pair of Miami dealers, using it as collateral for a $13 million loan from them, court documents claim.

In a text thread with Rechnitz and Mayweather, one of the dealers writes that he will “start to liquidate the merchandise” if he doesn’t receive payments soon, court docs show.

“Agreed thx,” Rechnitz responded instantly.

Mayweather later lamented the predicament in a text, writing, “I fought from a kid to get everything I own, and it’s sad that someone would even put me in this situation.” 

In November 2025, Rechnitz then urged Mayweather to execute a bill-of-sale for the jet, but the buyer’s name was left blank, the lawsuit says.

Mayweather has no idea who ultimately bought it and hasn’t seen a dime from the sale, the filing reads.

But he claims that “the proceeds were applied to a Bugatti-related obligation … with no portion paid to Mr. Mayweather.” 

Other shocking allegations of Rechnitz machinations include him ordering a lawyer to transfer a $15 million real-estate settlement to his friend’s Florida shell company and that he siphoned half of an allegedly illicit $16 million loan to himself.

A January email from Rechnitz allegedly shows that his nefarious scheme was ready to continue with 20 percent of nearly $4 million in distributions from Mayweather’s Manhattan real-estate portfolio going directly to him.