Instead of staying with Triple-A Indianapolis and taking the mound for the Indians, Karstens will undergo an evaluation by the Pirates' medical staff.
"We feel bad for Jeff," Pirates manager Clint Hurdle said.
Other than the natural expression of sympathy for the fan favorite and good teammate, there wasn't much else for the Pirates to say. This setback did not come as a shock, and it does little to alter the team's depth among starting pitchers.
While Charlie Morton and James McDonald continue to work their way back, aiming to somehow crack a rotation that is going strong, Karstens has been patient since first feeling discomfort in the shoulder before the start of exhibition play in Spring Training.
Karstens never made a Grapefruit League appearance, and ever since has been limited to bullpen sessions and simulated games. He was originally non-tendered by the Pirates, who re-signed him for $2.5 million in mid-January.
Tom Singer is a reporter for MLB.com and writes an MLBlog Change for a Nickel. He can also be found on Twitter @Tom_Singer. This story was not subject to the approval of Major League Baseball or its clubs.