Updated

Rookie pitcher Alex Reyes, one of the most highly regarded prospects in Major League Baseball, suffered a setback Tuesday when the St. Louis Cardinals sent him off for an MRI on his right arm -- the one he uses to throw baseballs.

Reyes had been scheduled for a throwing session on the opening day of spring training in Jupiter, Florida, but that session did not take place.

Manager Mike Matheny announced the news in Jupiter. He did not elaborate, other than to say "there must be a significant reason" for the MRI. GM John Mozeliak said Reyes had been experiencing elbow soreness prior to camp and that the team would wait until test results come back Wednesday to comment further.

In addition to his status for the season, Reyes' planned participation in the World Baseball Classic on the Dominican Republic team is in question.

Reyes, recently ranked as the No. 6 prospect in all of baseball by MLBPipeline.com, was considered a contender for the No. 5 spot in the St. Louis rotation or the bullpen. He went 4-1 with a 1.57 ERA and 52 strikeouts in 46 innings last season, just shy of the 50-inning threshold for rookie status for pitchers.