Mayweather was recently asked who his next opponent will be this September 12th. He responded that Andre Berto or Karim Mayfield are on his radar. He never mentioned Amir Khan or Kell Brook.
With Mayweather you never know if he is serious or just throwing out names to throw everyone else off. Andre Berto nor Karim Mayfield seem likely but they are young hungry fighters who are in their prime.
Andre Berto won his last fight by TKO over Josesito Lopez and in Karim Mayfield's last three fights he lost two. He won against an unknown Michael Balasi in an eight rounder and lost to Emmanuel Taylor & Thomas Dulorme.
Again Karim Mayfield.. seems very unlikely. As far as Berto, he could have fought Mayweather by know but his career has been very rocky.