The Cardinals designated Zimmermann for assignment before Game 2 of Tuesday's doubleheader against the Brewers.
Zimmermann coughed up three earned runs in five innings while working in bulk relief during the first half of Tuesday's twin bill, and he'll lose his place on the 40-man roster now that his services are no longer needed. Jared Shuster will come up from Triple-A Memphis in a corresponding move to add bullpen depth.