The Cardinals will call up Rajcic from Triple-A Memphis prior to Thursday's game in Kansas City, Jeff Jones of the Belleville News-Democrat reports.
St. Louis cleared a 26-man roster spot by previously sending Chris Roycroft down, though it will need to free a spot on the 40-man roster for Rajcic. The righty transitioned to a full-time relief role this season at Memphis and has thrived, logging a 2.88 ERA and 46:14 K:BB over 40.2 innings. Rajcic will be making his major-league debut when/if he gets into a game.