The Cardinals announced the move before the opener of their doubleheader Saturday against the Chicago Cubs. It wasn't immediately certain how much time Martinez will be sidelined, but general manager Michael Girsch called it a "very mild" strain.
Martinez struggled in his most recent outing Thursday, allowing six runs -- five earned -- in just five innings of the Cardinals' 9-6 loss to the Cubs. The two-time All-Star is 6-6 with a 3.39 ERA in 17 starts this season.
St. Louis' top pitching prospect Alex Reyes, who missed all of 2017 because of Tommy John surgery, made only one start this season for the Cardinals before suffering a lat injury that will sideline him for the rest of the year.
Information from The Associated Press was used in this report.