After four days of various exams in St. Louis, Carpenter was told that nerve irritation led to the weakness he was feeling in the shoulder earlier this week. That is separate from the bulging cervical disc issue that the club said was behind stiffness in the shoulder earlier in the month.
It is not, though, entirely unrelated to previous nerve issues that have cost Carpenter significant time in the past. General manager John Mozeliak characterized this nerve irritation as similar to that which forced Carpenter's season to end prematurely in 2004 and then, along with a separate recovery from elbow surgery, cost him almost all of the '08 campaign.
The length of Carpenter's absence was different for both.
"A lot of it came back down to putting him in a certain strengthening program to get that shoulder strong and stabilize it," Mozeliak said. "When that was accomplished, he was able to pitch pain-free. So a similar model will be used going forward."
For now the Cardinals are refraining from projecting any sort of timeline for Carpenter's return.
"I think I could throw something out there," Mozeliak said, "but it's never been helpful for me to do that, so I'd rather not."
The immediate plan for the 36-year-old Carpenter is for him to engage in exercises focused on restrengthening his shoulder. Surgery, Mozeliak said, is not being considered as an option right now.
Once Carpenter's shoulder is healthy, he will likely have to begin his throwing program from the start, thus it will take several weeks to condition his arm before a regular-season start becomes a possibility. That leaves the Cardinals having to prepare to move forward without one of their co-aces.
"I know it's not great news," manager Mike Matheny said. "We still don't know exactly how to take it."
One thing it means is that Lance Lynn's placement in the rotation has gone from tentative to temporary to indefinite in the course of a week. Mozeliak does not anticipate looking externally for a different starter, meaning that the club is confident that Lynn, who pitched as a starter in the Minors, is ready to handle the job at the highest level.
Carpenter, who left camp on Tuesday, is expected to return on Sunday or Monday. He visited several doctors during his time away, and it was through an aggregate of tests that the organization finally received some closure as to what was affecting Carpenter's arm.
Spring Training was progressing without issue for Carpenter until he threw to batters on March 3. Afterward he experienced what he described as stiffness, and he was subsequently shut down for 11 days. At the time the consensus was that a bulging disc was behind the discomfort.
Carpenter, who was coming off a season in which he threw 273 1/3 innings, resumed throwing and had a few successful bullpen sessions before enduring this latest setback on Monday.
"When I got excited was watching him throw the live [batting practice session] over there [last Sunday] and watching how the ball came out of his hand. He looked sharp," Matheny said. "I probably should have reined myself in a little to see how he responded the next day. That's when things started to go south."
If the Cardinals are looking for any consolation amid this news, it's that the five starters they will have to open the season have collectively put together a terrific spring. Adam Wainwright pitched five more scoreless innings in Friday's 2-1 over the Marlins, pushing his innings count to 14 for the spring. He has yet to allow an earned run.
Jake Westbrook has allowed one run and nine hits in his 15 innings, and Jaime Garcia bounced back from his one shaky spring start with five shutout innings on Thursday. Garcia struck out nine in that performance. Only one run has scored off Lynn in the eight innings he has put in as a starter. And aside from being stung by a few home runs, Kyle Lohse has had a successful spring.
"I think if you look at our staff as a whole, we'll do a good job picking Carp up," Wainwright said. "He's done that for years. It's time to return the favor."
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.