The Royals placed Zerpa on the 15-day injured list Wednesday with right knee discomfort, Anne Rogers of MLB.com reports.
The transaction comes after Zerpa exited his start Tuesday against the Angels with the knee injury following four innings of one-run ball. Zerpa looked as though he would line up for a two-start week, but the knee issue will thwart those plans. Jackson Kowar was called up from Triple-A Omaha on Wednesday to replace Zerpa on the active roster.