De Leon suffered a right lat strain in his outing at Triple-A Durham on Thursday, Josh Norris of Baseball America reports.
Norris noted a dip in velocity from De Leon before he was pulled from his outing and left the field with the training staff. De Leon's fastball was sitting in the 86-90 mile-per-hour range after being closer to 92 in his previous outing. Fortunately, there's no mention of a shoulder issue for De Leon, but the lat strain will still cause him to miss some time.