Johnson has made one Major League appearance, that coming in relief Aug. 18. The lefty allowed two earned runs in six innings of an extra-inning game before being sent down the following day because the Pirates needed a fresh arm.
The Cardinals are 15-20 in games started by an opposing left-hander.
Jenifer Langosch is a reporter for MLB.com. Read her blog, By Gosh, It's Langosch, and follow her on Twitter @LangoschMLB. This story was not subject to the approval of Major League Baseball or its clubs.