That prompted a visit to a Dallas-area physician, who confirmed the diagnosis.
"I do think this is one that we have to be really patient with," Cardinals senior vice president and general manager John Mozeliak said. "Unfortunately, it's going to be a few months. I think the best thing to do is let it heal and have aggressive rehab."
The Cardinals entered the spring cautious in their expectations for Walden, who missed the final five months of the 2015 season because of a rotator cuff injury. Walden opted for rehab over surgery last summer and came into Spring Training optimistic that he was once again strong.
But Friday's MRI not only revealed a tear in his latissimus dorsi muscle, but also a shoulder structure that Mozeliak described as "not sound."
"When one area is weak, you put more emphasis on the other," Mozeliak said. "In the end, both don't work. What's disappointing about it is how well he was throwing. Unfortunately, he's not someone who can go. I'm glad we added some depth."
Concerns about how Walden would recover from last year's shoulder injury prompted the Cardinals to sign Seung-Hwan Oh and Jonathan Broxton over the winter.
The Cardinals acquired Walden along with Jason Heyward in a November 2014 trade with the Braves, and signed the now-28-year-old to a two-year, $6.6 million contract shortly after that. He has thus far made 12 appearances for the team.
• Brayan Pena (left knee injury) is scheduled to be evaluated by the Cardinals' medical staff in St. Louis on Monday and then undergo a procedure on Tuesday to remove loose cartilage around his knee. Mozeliak said the length of recovery will likely be 2-4 weeks.
• Mozeliak said the club expects to get a better feel for how long Ruben Tejada (left quad strain) will be sidelined after Tejada relocates to Jupiter, Fla., this week to begin baseball activities.
• Starters Carlos Martinez and Jaime Garcia joined the team in Pittsburgh on Saturday night after each made extra spring appearances in Minor League games. Martinez said he threw about 80-90 pitches over seven innings on Saturday. "Everything is good," he added.
Jenifer Langosch is a reporter for MLB.com. Read her blog, By Gosh, It's Langosch, follow her on Twitter @LangoschMLB and like her Facebook page Jenifer Langosch for Cardinals.com. This story was not subject to the approval of Major League Baseball or its clubs.