Villarreal, a non-roster pitcher in the Royals' Spring Training camp, wants to concentrate on winning a bullpen spot.
"I want to make the team here with the Royals and I feel instead of being two or three weeks there, I want to be at practice here and be part of the team," Villarreal said.
Villarreal, from Nuevo Leon, missed more than two weeks of Atlanta's Spring Training in 2006 when he played for Mexico in the initial Classic. The team had a 3-3 record and played the USA twice, splitting decisions.
"It was one of the best experiences I've had with all the Mexican big leaguers together," he said. "It was unbelievable."
He pitched in two Classic games, working 2 2/3 innings and giving up just one hit -- a solo home run by Atlanta teammate Chipper Jones in a 2-0 loss to the USA.
Villarreal followed the Classic with a 9-1 record and 3.61 ERA in 58 games for the Braves.
This year he would miss at least 10 days for Classic practice and games, more if Mexico advances past the first round.
"It's hard to do but that's how it is. This is work," he said. "Sometimes you do it for the Mexico team ... but now it's for me and for my family. Next time, for sure I'll go."
The Royals have six other players in camp who are on the provisional rosters of Classic teams -- Joakim Soria (Mexico), Jose Guillen and Miguel Olivo (Dominican Republic), Mark Teahen (Canada), Mike Aviles (Puerto Rico) and Lenny DiNardo (Italy).
"Any time we can keep guys in camp, great. But this was [Villarreal's] decision, we don't persuade people one way or the other," Royals manager Trey Hillman said.
"I would imagine being with a new organization that he wants to be as visible and have as many opportunities as possible. It's certainly not going to hurt my feelings but I wouldn't have held it against him if he'd elected to go."
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.