"The good news is right now he's avoiding surgery," Mozeliak said. "The bad news is he's going to be out a while."
Mozeliak acknowledged that Walden first alerted the medical staff to some shoulder discomfort about two weeks before the team placed him on the 15-day disabled list last weekend with right biceps inflammation. Walden has been sidelined twice before by shoulder injuries in his career, though neither absence was long.
The Cardinals had taken an MRI of Walden's shoulder over the offseason after acquiring him in a four-player trade with the Braves and before re-signing him to a two-year deal. This latest MRI showed new trauma, which confirmed that Walden is not dealing with a preexisting issue.
Walden's herky-jerky mechanics may have contributed to some undue shoulder stress, and then there is also the question of usage. Walden opened the season by appearing in 11 of the team's first 15 games. While the Cardinals did have several off-days built into the early portion of their schedule, that workload raised some concern.
Walden's appearance on April 24 marked the seventh time in a 10-day stretch that he had pitched. He threw in back-to-back games four different times.
"Given his mechanics, I think there's just a lot of stress in that area," Mozeliak said to that point. "We knew that going in, but we're hopeful that we can still get a lot out of him."
In Walden's absence, the Cardinals have an eighth-inning setup spot to fill. Seth Maness will likely get the bulk of that setup work, though Matt Belisle and Kevin Siegrist will factor into the late-inning mix, as well. Due to overall workload concerns and a shortage of recent or upcoming off-days, Mozeliak said he expects to stick with an eight-man bullpen for some time.
"Very cognizant of it," Mozeliak said of stress the 'pen has been under lately. "The one thing that we have to do is position our bullpen with flexibility, which I think we have done. Having a starter go deep would be very helpful, for sure."
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.