Boxing fans have longed dreamed Mayweather and Pacquiao will repeat their epic fight of four years ago.
However, the unbeaten Mayweather, whose record stands at 51-0, has remained quiet over a possible return.
But Pacquiao is still boxing well at 40 years old and is due to fight Thurman on July 20.
And Khan thinks the only way Mayweather could be tempted out of retirement is by a destructive Pacquiao.
“For me, I think Floyd is done now. I don’t think Floyd will come back,” Khan told World Boxing News.
“Right now, I just can’t see him fighting again. I think he’s done.
“Maybe not in the sense he’s got nothing left.
“He’s probably got a lot left in him, but I just feel he’s made a lot of money in the game. So who is he going to come back and face?
“Maybe if Pacquiao beats Thurman in good style, then Mayweather might be interested. Maybe it could then be the ideal fight for him?
“Is it worth Mayweather coming back? – Maybe then it is.”
However, Mayweather is 42 years old and may not be able to perform to the level he is used to.
“If they do fight again, they’ll have people asking if Mayweather still has anything left against Pacquiao. I mean, Pacquiao is looking so good at his age (of 40),” Khan added.
“Also, that Mayweather has been out of the ring so long. Can he make a comeback and still beat him?
“You never know with Floyd. He loves that money and making a big paycheck. But I don’t think he’ll ever come back myself.”