The Cardinals announced today they will promote righty Michael Wacha to start Thursday against the Royals, tweets Danny Knobler of CBS Sports and others. The Cards had scratched Wacha from his Monday start in anticipation of the possibility of having him start Thursday in place of the injured John Gast. The Cardinals will need a 40-man roster spot for Wacha, but that can be opened easily by transferring Jaime Garcia to the 60-day DL.

Wacha, 21, was drafted 19th overall by the Cardinals last year out of Texas A&M, a pick the team received from the Angels as part of the compensation for the loss of Albert Pujols. Wacha made nine starts at Triple-A this year, posting a 2.05 ERA, 5.8 K/9, 2.6 BB/9, and 0.85 HR/9 in 52 2/3 innings. He'll be the fourth member of the 2012 draft class to reach the bigs, after Paco Rodriguez of the Dodgers, Kevin Gausman of the Orioles, and Michael Roth of the Angels. Prior to the season, Wacha ranked 76th on Baseball America's top 100 prospects list and the same on MLB.com's, failing to rank on Keith Law's list for ESPN. Law, however, elevated Wacha to #24 on a top 25 prospects list released today.

Baseball America ranked Wacha sixth among Cardinals prospects, as he was part of what they considered the best farm system in baseball given the presence of Oscar Taveras, Shelby Miller, Carlos Martinez, Trevor Rosenthal, and Kolten Wong. BA wrote that Wacha had the best changeup in the 2012 draft, adding, "It's easy to project him as a mid-rotation starter, and he could turn into something more if he finds a reliable breaking ball." He may have since found it, as Law wrote today, "Multiple scouts have told me they've seen an above-average breaking ball from Wacha this year, which was the main concern about him coming out of Texas A&M last June."

Will there be room in the Cardinals' rotation for Wacha beyond Thursday? Adam Wainwright, Lance Lynn, and Miller are holding down the first three spots, Garcia is out for the season, Chris Carpenter had a setback, and Jake Westbrook's elbow is improving. Tyler Lyons is in the rotation mix, Martinez could be at some point, and Gast could be as well when he's healthy.

If he stays up all year, Wacha will accumulate 123 days of big league service, making Super Two arbitration eligibility possible after the 2015 season. It's unknown whether that amount of service will put him within the top 22% of the two-to-three class at that point. Super Two players go to arbitration four times instead of the usual three, thus earning extra money.