"He's getting stronger. What he's done is he's long-tossing and throwing on the side," manager Ned Yost said.
There is no timetable for his return, nor any indication if he'll have to rehab in the Minors.
"He's garnering strength in his shoulder but we've got to get it so he can sustain it through a 30-pitch outing, and we'll go from there," Yost said. "He's getting stronger and getting more life on his pitches."