Oscar De La Hoya has branded Floyd Mayweather's mooted showdown with Conor McGregor a "farce" that could irreparably stain boxing.
Mayweather last weekend revealed he is "90 per cent" likely to come out of retirement to face UFC lightweight champion McGregor, who has a license to box in California and claimed he has already signed his contract to take on the American.
But former six-weight world champion 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.
Mayweather has diligently compiled a perfect 49-0 record and is widely regarded as the greatest fighter of his generation while his proposed opponent has never boxed professionally.
Even though the pair are arguably the highest-profile athletes in their respective fields and Mayweather has not competed since September 2015, De La Hoya has argued any boxing contest would be a complete mismatch.
In an open letter posted on Facebook, De La Hoya wrote: "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.
"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."