Contreras drove in two runs against his former team. He hit an RBI double in the fifth inning, and then was replaced by Ivan Herrera behind the plate before the Cubs batted in the sixth.
The Cardinals said Contreras is day-to-day.
The 31-year-old Contreras is batting .244 with 11 homers and 40 RBIs in his first season with St. Louis. He finalized an $87.5 million, five-year contract with the Cardinals in December.
The Associated Press contributed to this story.