Floyd Mayweather has challenged Amir Khan to beat Adrien Broner on the undercard of his bout with Marcos Maidana on May 3 in order to earn a fight with the pound-for-pound king.

The unbeaten Mayweather last week ended several weeks of speculation by choosing to face Maidana over Khan, who subsequently said his American foe was "running scared" after seeing his hopes of a big pay-day dashed.

While Khan has been kicking his heels on the sidelines for several months, last beating unfancied Julio Diaz on a close points decision nearly a year ago, many felt Maidana earned his shot at Mayweather with a surprise victory over Broner for the WBA welterweight title in December.

However, Khan's barbs at Mayweather may have had some impact, with the 37-year-old telling the Briton he can be next in line to fight him if the he can overcome his good friend and protege Broner.

"I don't have an easy fight on May 3, 2014, so I can't over look Marcos Maidana but Amir Khan, if you and Adrien Broner end up fighting each other on my show and you win (which you won't)… I'll fight you," Mayweather posted on Twitter.

Mayweather (45-0, 26 knockout wins) last defeated Saul Alvarez in September last year in a light-middleweight world title fight but will step back down to the welterweight limit in two months' time when he squares up against Argentinian Maidana at the MGM Grand in Las Vegas, Nevada.

See Mayweather explain why he chose to face Maidana instead of Khan in the video below.