The Cardinals optioned Romero to Triple-A Memphis on Wednesday.
Romero was dropped from the 28-man active roster to clear room in the bullpen for Jordan Hicks (neck), who was reinstated from the 10-day injured list in advance of Wednesday's regular-season finale in Pittsburgh. The demotion will make Romero ineligible to be included on the Cardinals' roster for the team's upcoming wild-card series with the Phillies.