Amir Khan spent years trying to nail down a showdown with Floyd Mayweather Jr yet the Briton is more than happy to see the undefeated multi-division world champion come out of retirement to face a man who has never had a single professional bout.

Mayweather hung up his gloves in 2015 with a 49-0 record but the 40-year-old American will return to the ring for a lucrative 12-round boxing match against Irish mixed martial arts champion Conor McGregor in Las Vegas next month.

Reports of a fight between former world light-welterweight champion Khan and Mayweather often surfaced in the media but the bout never materialised as neither camp came close to the negotiating table.

Despite plenty of criticism within boxing, the 30-year-old Khan feels the crossover fight between Mayweather and McGregor will be positive for the sport, which he feels has lost ground to the Ultimate Fighting Championship (UFC) MMA promotion.

"It's a business fight, one," Khan told Reuters. "Two, what's going to happen now is it's between boxing and MMA.

"At the moment, MMA and UFC is doing so many great numbers on TV, on pay-per-view. Boxing is doing OK but it took little bit of a dip. We are not getting the good pay-per-view numbers we used to.

"For now to combine both sports together is going to be great for the sport of boxing (more) than MMA.

"We hit a wall and we didn't really do anything. Boxing never moved forward around the world, whereas MMA kept moving forward and got bigger and bigger and bigger. Boxing kind of stalled in my opinion and we needed something like this."

Undefeated middleweight world champion Gennady Golovkin has dismissed the bout as a 'circus show' but Khan disagrees with the Kazakh fighter.

"You have to respect everybody that goes into the ring, you have to respect everybody who puts the gloves on. You have to fight in front of millions... not easy," the Briton said in an interview.

Khan, who won a silver medal as a lightweight at the 2004 Athens Olympics, is also hopeful that Mayweather's return could ultimately lead to a long-awaited showdown between the two men.

"When he beats McGregor, which I think he will, that fight can still be there. It really can happen," Khan (31-4) said. "There's still some big fights out there for me, Mayweather, (Manny) Pacquiao..."