UFC superstar McGregor has penned his portion of the contract for the superfight with Mayweather admitting last week he is "90 per cent" to come out of retirement to put his 49-0 unbeaten record on the line against the Irishman.
The fight looks set to break all box office records and could top £1bn in total purse but De La Hoya, who lost a close points decision to Mayweather when they faced off 10 years ago, is aghast that such a potentially highly lucrative bout could go ahead.
"To my fellow boxing fans: I write in the hopes that together we can protect the sport of boxing. With each passing day, it looks more and more likely that the circus known as Floyd Mayweather Vs. Conor McGregor will be coming to town in the near future," De La Hoya wrote in an open letter posted on Facebook.
"As undercard fights start to take form, athletic commissions give their blessings in exchange for millions of dollars and the fighters start counting even more cash, one group will eventually be left to make sure this farce doesn't occur. We, the fans, who are the lifeblood of our sport.
"I fully understand the initial attraction from any fan of combat sports. McGregor is almost certainly the best pound-for-pound MMA fighter. Floyd is Floyd - the most dominant boxer of his time. But success in one sport does not guarantee success in another. Far from it. And let's be clear, these are two different sports.
"Furthermore, it's not like McGregor would be fighting a good fighter, let alone a mediocre one. He would be fighting the best.
"To use a bit of an extreme analogy, I happen to be a pretty good golfer. Could I potentially hold my own on one of the second-tier tours? Maybe. But would I be able to compete with Rory McIlroy, Jordan Speith or Sergio Garcia? Of course not. Nor would I think to try."
Golden Boy Promotions chairman and CEO De La Hoya acknowledged those who would question his motives for writing such a letter.
Any Mayweather-McGregor showdown later this year could potentially overshadow his company's promotion of the Saul Alvarez-Gennady Golovkin bout in September.
But De La Hoya added: "My interest is in the health of boxing as a whole. Our sport might not ever recover."
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