Mayweather plans record-breaking 49th win in September against Berto

British welterweights Amir Khan and Kell Brook had both been hoping for a shot at the pound-for-pound king but Tuesday night's announcement looks to have put paid to those hopes.

"September 12, 2015 for number 49. Come be part of the history. Book your hotel and flights now," Mayweather tweeted, with a link to an Instagram post showing him and Berto and revealing the fight will take place at the MGM Grand.

Mayweather has long insisted his last fight would be in September when his current six-fight deal with Showtime expires, with Khan insisting at several points that a deal was close for a showdown between him and the American veteran.

"I don't think I have ever been closer to getting the fight with Floyd Mayweather than I am at this moment," Khan said at the start of June.

"The indications are that I have strengthened my case with my win over (Chris) Algieri and I believe there is every chance the fight could be confirmed within the next two weeks."

That never emerged, however, and it is Berto who will look to inflict a first defeat on the 38-year-old at the 49th time of asking.

Mayweather currently holds the WBA and WBC titles at 147lbs.

He was last in the ring on May 2 when he overcame Manny Pacquiao in the most lucrative fight the sport has ever seen and, while talk of a rematch instantly emerged, the Filipino has since undergone shoulder surgery that could rule him out for up to a year.

American Berto, who will be 32 when the pair meet, was undefeated in his first 27 fights but has suffered three losses in his last six to take his record to 33-3.

Khan - a stablemate of Berto - insists there is still plenty for him to look forward, despite another snub from Mayweather.

He said: "I’m disappointed not to have got the fight for what is the third time after having been one of the frontrunners. However, there are many big fights out there for me and I’m going to continue working hard to establish myself at the top of the welterweight division.

"Floyd Mayweather has fought the biggest names throughout his career and has earned the right to face whoever he chooses. I wish my stablemate Andre Berto and trainer Virgil Hunter the very best of luck in the fight. I have seen how hard Andre trains and works and know that he is ready to give Floyd a very tough night."