Matz suffered a left knee strain in Saturday's start against the Reds, John Denton of MLB.com reports.
Matz left Saturday's outing with what was originally reported to be a right ankle injury, but it has now been determined that he strained his left knee while trying to field a ball at first base in the sixth inning. Unfortunately, the left-hander will likely be placed on the 15-day injured list after making just one start since his last trip to the IL.