The right-hander had to leave his Indianapolis start against Lehigh Valley after three innings with tightness in his right shoulder. Morton was scheduled to go six innings or throw 90 pitches in the fourth of his five rehab starts. Instead, he was removed after 49 pitches, without allowing a hit.
Morton is returning to Pittsburgh for further medical evaluation. He was due for one other Minor League outing and had been penciled by manager Clint Hurdle into the Bucs' rotation for a May 14 start.
As for Karstens, he threw a two-inning simulated game Friday afternoon at PNC Park, and said everything "felt good" after he worked on all of his pitches.
Karstens is tentatively scheduled to fly on Monday to Florida, with his first two outings scheduled for Wednesday in extended spring camp, and for May 13 with Class A Bradenton.
That timetable puts the veteran righty on target to possibly step up to Indianapolis for the ensuing rehab start.
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. Andrew Simon is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.