A potential fight between Juan Manuel Marquez and semi/un-retired Floyd Mayweather Jr. is being talked about for September, but weight is an issue. From ESTO via Boxing Scene:
Mayweather wants the fight to take place at the welterweight limit of 147, and Marquez, still at 135, is not willing to move up that high in weight. Marquez feels that anything above 140 pounds will put him at a huge disadvantage.
Marquez is correct, it'd be too big for him. Floyd's not really a welterweight himself, but he's a bigger man than Marquez, who is really a blown up featherweight that could probably still make 126 pounds if the money was there. As great as he was against both Joel Casamayor and Juan Diaz, 135 seems to be stretching him just a bit thin as it is.
There's also only one reason I can think of why Mayweather can't make 140. Relatively speaking, making 147 should be a cakewalk for Floyd. 140 would simply require him to put in extra work, which might be a problem given the nagging little injuries he's had over the years, a lot of which spark up in his training.
If Marquez-Mayweather goes down the tubes (which kind of seems likely), Marquez might drag another guy out of retirement: Erik Morales. I have so little interest in watching Marquez beat the crap out of Morales that I can't even properly put it into words. Marquez is accepted as being on the level of Barrera and Morales historically at this point, or at least he should be. There's no reason for Marquez-Morales. JMM would be picking the bones of an increasingly-delusional legend, who is flat washed-up and turns 33 in September, when Marquez plans to fight again. 33 isn't old, and it certainly isn't old in today's boxing world, but Morales has years of wars that have piled up. He fought a close fight against David Diaz, but that's part of the problem. Prime Morales would've wasted Diaz with little trouble.
Bob Arum and Top Rank have been in touch concerning Edwin Valero, but Nacho Beristain says that Marquez "has no interest in fighting Valero." It makes sense. There's little money in it and Valero is dangerous.
But going back to Marquez-Mayweather: It's kind of cliche to say, but Juan Manuel called Floyd out, not the other way around. A lot of people are saying this, and I think it's sort of valid. If this fight doesn't come off, don't blame Floyd out of habit. In fact, probably don't blame anyone. It was half a pipe dream to begin with.