Montero, along with teammates Henry Blanco and Gerardo Parra, paid a visit to the UCLA campus, where Real Madrid, a professional soccer team based in Spain, was practicing.
Though Montero grew up in Venezuela, both of his parents are from Spain and he is a big fan of Real Madrid -- and in particular its goalkeeper, Iker Casillas.
"He was nice, man, really humble guy, down-to-earth guy," Montero said. "It really surprised me how his personality is. I talked to him for a half an hour and he was an unbelievable guy."
The D-backs have an off-day Thursday, so Montero, Blanco and Parra are staying in Los Angeles to watch Casillas and his teammates play the Los Angeles Galaxy in an exhibition match.
Montero was going to purchase tickets, but Casillas told him he would get them for him.
"He knows what baseball is, but he doesn't follow it," Montero said. "We just wanted to meet him because he's a superstar, well known throughout the world."