Floyd has already proven that fighters with pisspoor defense will get dissected, no matter how much heart they have (Gatti, Corrales). The fighter I see being most problematic for Mayweather is Paul Williams because of his size and workrate and if he matched up right now with Cotto and beat him I'd say he has the chutzpah to call Mayweather out. The only other fight out there right now for PBF is Cotto.