McCullers was placed on the 15-day DL on Wednesday with elbow discomfort.
One of the Astros' top prospects, Joe Musgrove, will take McCullers' spot in the rotation and start against the Rangers on Sunday. This is a major blow for the Astros, as McCullers has as much talent as anyone in that rotation. The term "discomfort" doesn't provide much for owners to work with, and his official status could change in the coming days. It's safe to say he could be headed for a lengthy absence.