Amir Khan will be one of many ranging from fighters to fans dismayed by Floyd Mayweather's selection of Andre Berto as his final adversary before entering retirement.

Reaction ranging from anger to incredulity has greeted Berto's confirmation as the 49th opponent - and almost certainly 49th victory - of Mayweather's career on September 12 in Las Vegas.

Mayweather has adopted a risk-free approach to what he claims will be his final outing, selecting a former world champion who has lost three of his last six contests, one of them to a man who had been defeated 10 times.

Berto was on the wrong end of clear points decisions against previous Mayweather victims Robert Guerrero and Victor Ortiz and is rated a 16/1 underdog against the 1/100 favourite.

Only one more win is needed for Mayweather to equal Rocky Marciano's fabled record of 49-0 and the 38-year-old WBA and WBC welterweight champions is taking the easy route to his place in the history books.

Agreeing to face Manny Pacquiao five years too late was forgiven due to the sense of relief that the two greatest boxers of their generation were fighting at all, but by picking such a low calibre adversary in Berto the self-anointed 'The Best Ever' has invited ridicule.

Khan was heading a queue of worthy opponents hopeful of meeting the world's highest-grossing sportsman and was convinced he had manoeuvred himself into the number one contender position.

Danny Garcia and Keith Thurman were equally viable alternatives to Khan and the trio will have greeted the selection of Berto from boxing's deepest and most talented division with the same disbelief seen on social media and message boards.

Reports that Mayweather was considering a catch-weight showdown with Gennady Golovkin can only have been fantasy given the gulf in class between the popular middleweight knockout specialist and Berto.

"I'm ready to prove again to the whole world why I'm The Best Ever. I always bring my A-game and this fight against Andre Berto is no exception," Mayweather said.

"He's a young, strong fighter who is hungry to take down the best. Forty-eight have tried before and on September 12 I'm going to make it 49."

Mayweather is adamant it will be his final fight but few believe him and few care, as his desire to protect his unbeaten record at all costs makes his clash with Berto a pay per view event to avoid.