NEW YORK - A possible bout between retired unbeaten boxing champion Floyd Mayweather and mixed martial arts titleholder Conor McGregor is getting lots of buzz, but one of Mayweather's former opponents said on Tuesday the crossover tilt would be a black eye on boxing.

McGregor has been challenging Mayweather to a fight for months, but the two have yet to reach terms while both have been doing their part to drum up interest with plenty of back and forth in the media.

"It's a joke for boxing if that happens," said WBO super welterweight champ Canelo Alvarez, who dropped a majority decision to Mayweather in 2013.