Amir Khan's repeated public challenges have cost him a shot at Floyd Mayweather Jr, according to the undefeated American's uncle Jeff Mayweather.

Two-time world champion Khan has been relentless in his quest to secure a fight with the welterweight king for the past 18 months but on each occasion has been passed over.

Mayweather has just one more fight left on his current Showtime contract and appears content to retire after that 12 September date. In early June, Khan said he was hopeful of securing that slot, suggesting he was closer than ever to securing a showdown with the 38-year-old.

With Mayweather unresponsive to his claims, Khan claimed he then spoke to the five-weight world champion's father and trainer Floyd Mayweather Snr over the telephone and felt he was now under the skin of his would-be opponent and his camp.

But with Mayweather now looking likely to end his career with a bout against Andre Berto in September, Jeff Mayweather has told the Briton his repeated public challenges have got him nowhere.

"I think he killed the fight, because he started talking too much," Jeff Mayweather told On The Ropes. "It got to the point where he probably got under Floyd's skin enough for him to say: 'F**k you, I am not giving you a fight, not because I can't beat you, just because I am not gonna give you the payday like everyone else is begging for.'

"Amir Khan started acting like Floyd needed him. Really? He needs you? For what?"

Undefeated middleweight Gennady Golovkin is also keen for a meeting with Mayweather and has even offered to drop down a weight to boost his chances.

But according to TMZ Sport, there is already a deal in place for Mayweather to take on former IBF and WBC welterweight champion Berto in Las Vegas, where a victory would see him equal Rocky Marciano's long-standing record of 49-0 before retiring.