Karstens declined to comment on his condition, passing word to "just go with the shoulder discomfort," but Pittsburgh general manager Neal Huntington confirmed the pitcher suffered a "flareup of the biceps tendinitis" that sidelined him a month ago.
And, just like that, competition for the Bucs' rotation morphed from a match race to all-out scramble among five other candidates:
• Jeff Locke, the lefty who appeared to already have an inside track for the lone opening.
• Jonathan Sanchez, the veteran lefty whose opt-out clause -- triggered Sunday morning -- takes on a whole different perspective.
• Jeanmar Gomez, who, unlike Sanchez, already is on the roster and has been very effective (seven innings, one run) in his last two outings.
• Kyle McPherson, who may most benefit from Karstens' setback, with a Mulligan for his discouraging last start (10 hits and nine runs in 4 2/3 innings against the Braves).
"We've kept four guys stretched out as Plan B, hoping we wouldn't have to use Plan B," Huntington said. "Looks like we'll probably have to. Now it's a decision between four for two, instead of four for one."
The most pressing decision concerns Sanchez, who has not allowed a run in his past two starts, allowing three hits and one walk in eight innings while striking out seven. The Pirates need to decide whether to place him on their 40-man roster or grant his release Tuesday before that day's game against Toronto. So manager Clint Hurdle, pitching coach Ray Searage and Huntington will have to make that decision based on what they've already seen.
Huntington talked optimistically Friday about Karstens' chances to answer the Pirates' first call for a No. 5 starter on April 7. "If Jeff is able to make all his outings between now and then," Huntington had said, "he should be fine."
"We needed every bit of the remaining [Spring Training] schedule to get Jeff stretched out to be able to make that [April 7] start," said Huntington, who was not yet ready to confirm that Karstens was headed to the DL. "Most likely, but we still don't know the long-term prognosis. Or even the short-term. Is it just a temporary setback? Does inflammation need to get out?"
Huntington isn't likely to peruse the list of available pitchers -- that market will continue to grow in the coming days as Opening Day approaches and teams make personnel decisions -- with anything more than passing interest. In addition to the quartet of candidates in camp, the Pirates have two rehabbing veterans in Francisco Liriano and Charlie Morton.
"If we didn't have them waiting in the wings for May or June, there may be more intent [for acquiring reinforcement]," Huntington said. "We feel comfortable with the four guys competing for the final two spots and the other guys on the horizon."
And yes, the general manager was including Gerrit Cole in the horizon group.
Karstens was first shut down with biceps tendinitis early on Feb. 19. He made a steady recovery, beginning with a March 5 bullpen session, and made two appearances in Minor League games. His latest outing was Monday, when he came away from a four-inning, 50-pitch start feeling fine and even talking enthusiastically about a new over-the-head windup that "reduces pressure on my shoulder."
"Today was the first time he got to the point where he felt like he needed to make us aware that he couldn't pitch," Huntington said.
Concerns over Karstens' durability had prompted the Pirates to non-tender him. However, the two sides negotiated a new deal, coming to an agreement on Jan. 17 with a guaranteed base salary of $2.5 million.
When healthy, Karstens has been one of the Bucs' most proficient pitchers the last two seasons, the only one to pitch to a sub-4.00 ERA in both 2011 and 2012.