Donald Trump may want to build a wall across the U.S. southern border to keep Mexican migrants out but don't expect Mexico to pay for it, former President Felipe Calderon told CNBC, calling the billionaire a "not very well-informed man." The GOP presidential hopeful insisted in October that if elected, he would build a wall along the Mexican border and get Mexico to pay for it. But Calderon, Mexico's president from 2006 to 2012, told CNBC on Saturday that there was no way that Mexico would pay for it. "Mexican people, we are not going to pay any single cent for such a stupid wall! And it's going to be completely useless," Calderon said. "The first loser of such a policy would be the United States," he said. "If this guy pretends that closing the borders to anywhere either for trade (or) for people is going to provide prosperity to the United States, he is completely crazy."

Former Mexican President Felipe Calderon CRIS BOURONCLE/AFP/Getty Images

When announcing his presidential bid last June, Trump said "the U.S. had become a dumping ground for everybody else's problems," and called out Mexico as a particular culprit. "When Mexico sends its people, they're not sending their best. ...They're sending people that have lots of problems, and they're bringing those problems with us. They're bringing drugs. They're bringing crime. They're rapists. And some, I assume, are good people," Trump said.

Calderon questioned the caliber of candidates like Trump, who has offended large sections of the population , including Muslims by calling for a temporary ban on Muslims entering the U.S., as well as attracting a large following during his presidential bid.

"It is incredible that a quite admirable society like the American society could produce such kind of candidates," Calderon said. "I cannot understand that. No offense, no offense to America. So Donald Trump … is ambitious but not exactly very well-informed man, I don't want to say ignorant, but he is not very well informed." Calderon said the level of migration of the Mexican labor force to the U.S. had been steadily declining.