LAS VEGAS: Boxer Floyd Mayweather agreed to a crossover fight with mixed martial arts champions Conor McGregor because his fans wanted it, the 40-year-old has said.

Mayweather, who retired in 2015 with an unbeaten record of 49-0, and UFC lightweight champion McGregor will clash in a 12-round fight in Las Vegas on August 26 after teasing the event for nearly a year.

"McGregor is a tough competitor. People all around the world demanded this fight so I had to give them what they wanted to see," Mayweather is quoted as saying by sports website BlackSportsOnline.com.

"They asked for this fight. I was in retirement, but they wanted me back and I'm back."

The multi-division boxing world champion is favourite to beat McGregor, who never boxed professionally, in Las Vegas.