Villar, 22, was called up from Triple-A Oklahoma City following Sunday's game after hitting .278 with 16 doubles, eight triples, eight homers, 41 RBIs and 31 stolen bases in 90 games this season. Manager Bo Porter said Villar will be given every chance to show what he can do at the position.
"It's sink or swim," Porter said. "You look at the skill sets, and the skill sets will tell you he has an opportunity to be successful. We're in a position we can give him the opportunity, and if there are struggles we can stick with the struggles, because we believe at the end of the day the skill sets are going to show through."
Villar is the fourth player to start at shortstop this season and will give the Astros a much-needed speed presence. Tyler Greene came to spring camp as the starter, but was cut in March when Ronny Cedeno was signed. Marwin Gonzalez has started 46 games at short, Cedeno 37 and Jake Elmore 14.
"Instead of waiting to September, we have the lion's share of the season left, and why give those at-bats to anyone else than the guy we believe is going to be the starting shortstop next year?" Porter asked.
Villar said on Monday he wouldn't be nervous for his debut, saying he played alongside Major League players and in front of big crowds in winter ball in his native Dominican Republic.
"For me, it's the same game," he said with a smile. "Maybe I get two or three base hits, I don' t know. Maybe two stolen bases."
Brian McTaggart is a reporter for MLB.com and writes an MLBlog, Tag's Lines. Follow @brianmctaggart on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.