"We got the report and we're going to treat him and take care of him medically," Pirates' manager Clint Hurdle said. "There will be no throwing for seven to 10 days and then we'll go back to building him up.
"We'll take it one step at a time, he's got to get well enough to throw first and then we've got to get him back out on a rehab assignment, start off with a number of pitches that we are comfortable with and then build him back up to close to 80 to 100 pitches. I can't give you a timetable.
Right-hander Brad Lincoln is tentatively scheduled to make a spot start on Monday against Colorado, taking Karstens' spot in the rotation.