Floyd Mayweather says he got cleaned out to the tune of $175M … claiming a former close associate ran a years-long scheme that allegedly drained his bank accounts, hijacked real estate deals, pawned off his jewelry and even made his private jet disappear.

According to a bombshell lawsuit, obtained by TMZ Sports, Floyd claims Jona Rechnitz spent years gaining his trust … before allegedly becoming the boxer’s de facto money manager, real estate guy and banking middleman.

Now, Mayweather says it was all one giant setup.

Among the jaw-dropping claims … Floyd says roughly $100M worth of bling was handed over to Miami jewelers for only about $13M in return … and says a huge chunk of the collection is still sitting with the dealers.

The lawsuit even includes an alleged text exchange where a jeweler threatened to start liquidating Floyd’s pieces if payments weren’t made … and Rechnitz allegedly replied, “Agreed thx.”

Mayweather also says he wired $7.5M into what he thought was an investment deal … but claims the investment never happened and the money disappeared. Beyond that, he alleges another $15M tied to a realty settlement was transferred out without his permission.

And it doesn’t stop there … he says he unknowingly signed paperwork transferring ownership of his Gulfstream jet with the buyer section left blank … and says he still doesn’t know where the aircraft money went.

Floyd further accuses Frist of falsely presenting himself as a top executive of Vada Properties despite allegedly never holding those positions.