Nacho Beristain is looking forward to Juan Manuel Marquez's upcoming showdown with Mike Alvarado on May 17 at the Forum in Los Angeles—a fight that could lead to a fifth showdown between Marquez and Manny Pacquiao.

But if Beristain were to have it his way, the trainer said that he will not allow Marquez to face Pacquiao again, pointing out that he can't see any reason to face the former pound-for-pound king again aside from his fighter's fifth-title aspirations.

Marquez previously turned down numerous proposals to fight Pacquiao in a fifth showdown, but Top Rank Promotions boss Bob Arum has been pushing for the rematch.

Arum recently announced that the winner of the Marquez-Alvarado showdown will face the winner of the WBO welterweight title showdown between Pacquiao and Timothy Bradley next month in Las Vegas.

"What Juan Manuel wants more than anything is this [fifth] championship [at welterweight], and that's why the name of Pacquiao is once again [being discussed]," Beristain told BoxingScene.

The veteran trainer pointed out that their sixth-round knockout win over Pacquiao in December 2012 is more than enough to justify that Marquez is better than his Filipino nemesis.

And if Marquez really wants to win a title in a fifth weight class, Beristain said that the 40-year-old Mexican should look into the other champions from another sanctioning body aside from the World Boxing Organization.

"I believe that if he gets past [Alvarado], Juan Manuel can fight for [a world title from] another sanctioning body. There is no reason for him to face Pacquiao again, who he already conquered with that tremendous knockout," Beristain stressed.

But before thinking about winning a fifth title, Beristain added that Marquez should gear up for a tough showdown with Alvarado, who is also looking to bounce back from his loss to Ruslan Provodnikov in October last year.

The 74-year-old trainer said that he supported Marquez's decision to face Alvarado, but he admitted that the 33-year-old former light welterweight champion will be a tough nut to crack.

"He is a difficult opponent for a fighter like Juan," Beristain said of Alvarado. "Alvarado is a tremendous puncher. It's ideal for Juan to provide a big fight to the public, but [this one is] dangerous, because [Alvarado] is young and strong."