JUPITER, Fla. -- Cardinals top-ranked pitching prospect Alex Reyes will miss the 2017 season after an MRI revealed a complete tear of the ulnar collateral ligament in his right elbow. He had Tommy John surgery Thursday.
The news, which comes on the second day of camp, leaves the Cardinals with a shrinking pool of starting pitchers and facing a year ahead in which one of the early National League Rookie of the Year Award favorites will not take the mound. Reyes, 22, will require an estimated 12 to 18 months of rehab before returning to competition.
"It's obviously very disappointing," general manager John Mozeliak said Wednesday. "We had very high expectations for him, but I guess if you're going to look from a timing standpoint, he has a year to do his rehab and get everything that he's dealing with under control. And hopefully he'll be back better than ever."
• Posnanski: Reyes dealt arduous challenge
Reyes underwent the imaging test on Tuesday after notifying the Cardinals late last week of elbow discomfort. Reyes said he became concerned after throwing an offspeed pitch during a bullpen session and then feeling "a pain throughout my elbow that I hadn't felt before."

Team physician Dr. George Paletta examined the MRI results and informed Reyes on Wednesday morning that Tommy John surgery would be needed. The images were also sent to Dr. James Andrews for a second opinion.
"It [stinks] to go through this and miss an entire season, but if those are the things that have to happen for me to get back on the field at 100 percent, then that's what we have to do," Reyes said. "It [stinks]. You want to be on the field. But that's something that can't happen right now."
"You have to remain optimistic and positive," Mozeliak said. "When you think about timing, sure, it's not great. But when is it ever great?"
• Rogers: Reyes' injury a tough start for Cards
The image of Mozeliak announcing a season-ending injury to one of his players under the backdrop of the team's spring complex has become a frustratingly familiar one for this organization. In recent years, Mozeliak has stood in the same vicinity and declared Adam Wainwright (2011), Chris Carpenter ('13), Rafael Furcal ('13) and Jason Motte ('13) out for the season before the team played its first game.
Reyes, ranked by MLBPipeline.com as baseball's No. 3 pitching prospect and No. 14 prospect overall had incurred elbow trouble before. He was sidelined for more than two months in 2013 due to an elbow strain, but had pitched without further discomfort in that area until recently.
Not only will this surgery wipe out Reyes' season, but it will also preclude him from representing the Dominican Republic in the World Baseball Classic.
"I'm just kind of taking it in, will go through the process and do the rehab," Reyes said. "There are a lot of guys who have been through this surgery. The success rate is high. It's something I definitely look at."
Though Reyes was not assured of an Opening Day rotation spot, he was ready to compete for one. And the Cardinals weren't shy in expressing optimism that Reyes would make critical contributions to the Major League team at some point this year.
The right-hander appeared in 12 games (five starts) for St. Louis last season and posted a 1.57 ERA with 52 strikeouts in 46 innings. Reyes was moved permanently to the rotation in mid-September and led the team to wins in each of his subsequent starts.
"Obviously, a kid that came in and did so much in such a short period of time and made a big splash in our organization to open the eyes of the league, that's a hard thing to do," manager Mike Matheny said. "He's young, and this might be an opportunity for him to, in the long run, maybe even be stronger from it. Just not great news, obviously, today."
As for the Cardinals' pitching plans, their attention pivots to a trio of pitchers -- Michael Wacha, Luke Weaver and Trevor Rosenthal -- who will vie for one opening in the rotation. Wacha, based on recent comments from Mozeliak and past performance, appears to have the inside track, as long as he remains healthy.
"Overall, I feel like we still have that depth," Mozeliak said. "That's why we collect it."