Matthews will be called up from Triple-A Memphis to start Saturday against the Blue Jays for his MLB debut, Derrick Goold of the St. Louis Post-Dispatch reports.
Matthews was removed as the probable pitcher for Memphis on Thursday, which hinted at his promotion. He has been stellar in Triple-A since the start of June with a 1.55 ERA across 52.1 innings. The left-hander is joining the big club as a sixth starter for now, but a full-time rotation spot could open soon if Dustin May is traded ahead of Monday's deadline.