McCullers was placed on the 10-day disabled list Monday due to back discomfort, Brian McTaggart of MLB.com reports.
It's unclear when the issue cropped up, but it may explain why he's been so bad in the month of July. Since the calendar turned, the young starter hasn't pitched deeper than five innings in any game, accumulating a 9.64 ERA for the month. A timetable for his return has not been established yet, but Brad Peacock seems like a logical candidate to pick up starts in his stead.