Amir Khan
Amir Khan's hopes of clinching the career-defining bout have been all but extinguishedGetty Images

Floyd Mayweather Jr has all but ended Amir Khan's hopes of facing the unbeaten American before his retirement after announcing he will call time on his career after one final fight in September at the MGM Grand.

Mayweather has two fights remaining on his Showtime Television contract and has no plans to renew the deal beyond the end of the year.

But the timing of 38-year-old's last fight in the early autumn rules out Khan, as the prospective training period before a potential bout conflicts with Ramadan, the Islamic month of fasting, which has previously scuppered the Briton's hopes of clinching the career-defining fight.

"My last fight is in September," Mayweather said during an open training session earlier in April. "I don't enjoy it like I once did. It is at a point where it is business. It is my job.

"I go to the gym, I train. I know what I have to do. There was a time when it was fun but I am to a point now where I am really over all of that stuff. Final one [fight] at the MGM Grand in September."

Khan will face Chris Algieri on 29 May in his next fight and the news regarding Mayweather's exit from the sport means an all-British meeting with Kell Brook before the end of 2015 remains a distinct possibility.

Brook will make the second defence of his IBF welterweight crown against Frankie Gavin 24 hours after Khan fights in New York.

And despite announcing his first fight of the year, Khan has used the news as an opportunity to take another shot at the Sheffield-born fighter, who has questioned the standard of opposition facing the former two-time world champion.

"How can Kell knock Algieri given the quality of men he has boxed while there is no-one of note on Gavin's record?" said Khan. "Algieri has shared the ring with some tremendous fighters. Manny is a huge, very difficult fight for anyone but I know I'll have to be at my best on the night."