Marquez, 42, last fought in May 2014, beating Mike Alvarado by unanimous decision to take his professional record to 56-7-1.
Cotto (40-5) lost his lineal middleweight title to Saul Alvarez in his last fight in November, and Beristain believes Marquez could make a good fight with the Puerto Rican, despite his recent inactivity, per Fox Deportes (via Elisinio Castillo of BoxingScene.com):
[Marquez] has never closed the door [on fighting again] and he's made no decision to retire from boxing. I have not spoken with Juan Manuel for three months, but I know him and he's never had any problems with inactivity. He can still return straight to training.
I do not rule out [this version of Marquez] being capable of fighting against Cotto. If [Marquez] returns to the ring, I don't think it is unreasonable to do it with an opponent of that level. It would be a good fight, given their styles.
Cotto's trainer, Freddie Roach, recently said he would like to see his man drop back down to welterweight—the Alvarez clash was fought at a catchweight of 155 pounds—in order to face Marquez, per Boxing News' George Gigney.
Despite losing to Canelo by unanimous decision, the 35-year-old put in a decent performance, as can be seen below:
He most certainly still has plenty left in him, and a clash with four-weight champion Marquez has the potential to be a fantastic fight.
Cotto himself has won world titles at four different weight classes, but he has not fought at welterweight since his 12th-round knockout defeat to Manny Pacquiao in 2009.
Per Castillo, Marquez has never weighed in higher than 144.5 pounds in any of his welterweight fights, including his various clashes with Pacquiao.
They are both accomplished, exciting fighters who have no problem with being aggressive when necessary.
If, as Beristain insists, Marquez is ready to make a quick return to the ring to face Cotto, boxing fans could be in for a treat in 2016.