Karstens had returned to the mound last Tuesday and pitched well in the team's win over Chicago. However, during his bullpen session late in the week, Karstens once again felt the same arm discomfort that had caused him to miss a start less than two weeks earlier.
The Pirates are not ruling out Karstens' ability to return before the end of the season. But it's not guaranteed that he will, either. That determination will be made once the Pirates see how Karstens' shoulder responds to rest and treatment.
Karstens did have his shoulder examined and no structural damage was found.
"It just doesn't feel right," manager John Russell said. "It's been a long year for him, and it's a little cranky."
The Pirates were already going to be cautious with how much Karstens pitched during this last month given that he has thrown more innings (121 1/3) than in any year since 2006. And as general manager Neal Huntington noted on Sunday, the fear that Karstens might wear down at the end of the season was one of the reasons why the organization initially saw the right-hander as fitting best in the bullpen.
"He's not the most physical guy," Huntington said. "He doesn't do it the easiest. But I'll tell you what, he's given us everything he's had every time he goes out. He's shown us that there is definitive value. He's shown us that Jeff Karstens can get Major League hitters out. For many periods this year, he was our most consistent starter."
Though Karstens' future with the organization might not be as a starter, he came up big for the Pirates in that role on a number of occasions this year. Thrust into the rotation at the end of April, Karstens became a permanent part of it beginning in June. He posted a 4.88 ERA in 25 games (19 starts) after not beginning the season on Pittsburgh's 40-man roster.