amir khan has rejected a £ 5million fight with kell brook in june .
khan claims that brook only wants to fight him for ` one big payday '
brook will struggle to fight one of boxing 's big names , according to khan .
khan says brook is nowhere near floyd mayweather and manny pacquiao .
watch here : mayweather vs pacquiao official advert released .
freddie roach : pacquiao better equipped to beat mayweather than in 2010 .
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