The MRI reading confirmed the injury to be similar to the one Garcia dealt with earlier this season, though the left-hander said on Tuesday that the symptoms feel different. He will be re-examined by orthopedic surgeon and Mets team doctor David Altchek on Thursday to get a second opinion.
The visit will help to determine whether Garcia will need to undergo shoulder surgery to address the issue, which Garcia attempted to mitigate with only rest and rehab this summer.
"I am concerned because I know it's something I've been battling the last year," Garcia said after the Cardinals' workout at Nationals Park on Tuesday. "But at the same time, I have a lot of faith that whatever happens with my arm is going to be good. I'm going to work as hard as I can to come back from anything. I'm just going to stay positive. We'll see what the doctor has to say now and hope for the best."
The left-hander lasted just two innings in his Game 2 start on Monday, notifying staff after the second inning that he was feeling left shoulder discomfort. He also informed them his shoulder hadn't been feeling right for several days.
Garcia said on Tuesday that he believes the issue began late in his final regular-season start, which came Oct. 1 against the Reds. He pitched 6 2/3 innings in that game and threw his side session, as scheduled, four days later. Though his arm didn't feel right then either, Garcia did not let anyone know.
"I've had stuff in my shoulder happen before where it hasn't been 100 percent," Garcia said. "I wanted to learn how to pitch with a little something in my shoulder and be fine with it. I thought it was one of those things. It's the playoffs. I want to be there for my team. I want to be able to help out. But I realized once the game started that it never got better and I had to say something."
General manager John Mozeliak, while not specifically critical of the way Garcia handled the situation, reiterated on Tuesday that the team urges full disclosure when it comes to medical issues.
"You still have to admire the fact that he wanted the ball," Mozeliak said. "Obviously, we try to promote transparency when it comes to the medical side. For whatever reason, we didn't get all the details. He tried. That's all we can ask."
Garcia missed more than two months with a left shoulder injury this season, though this is the first time since his mid-August return that he let on that anything was wrong. In his nine starts after coming off the disabled list, Garcia went 4-5 with a 3.25 ERA.
"In those starts, it was just normal discomfort -- being tight and taking a little time to get warm, time to recover between starts," Garcia said. "But I was pitching some of the best [I have] in the last couple of years.
"This," he added, "was a different thing."
Miller, ranked by MLB.com as the Cardinals' No. 2 prospect, becomes the third rookie in the Cardinals' bullpen. He also helps add depth to a 'pen that could be without Lance Lynn for the rest of the series. Lynn threw 50 pitches in relief during Monday's 12-4 win and would likely be the one to take Garcia's spot in the rotation should the Cardinals advance past the NLDS.
By coming off the roster mid-series, Garcia would not be eligible to return until the World Series. However, the Cardinals have no expectation that the 26-year-old will be ready to pitch before 2013. Shoulder surgery would obviously also jeopardize next season for Garcia, who is signed with St. Louis through 2015. The club holds club options for the two seasons after that.
"When you work as hard as he has, your goal is to be pitching now as a part of a postseason roster," Mozeliak said. "I can definitely tell when I met with him this morning that he was down, he was frustrated. From a practical standpoint, the club has to think of the short-term view at the moment. What Jaime has to think about is more getting ready for next season."
Jenifer Langosch is a reporter for MLB.com. Read her blog, By Gosh, It's Langosch, and follow her on Twitter @LangoschMLB. This story was not subject to the approval of Major League Baseball or its clubs.