Before the season even began, the Cardinals released the bad news that Carlos Martínez experience a setback in his training over the offseason and his 2019 debut would be delayed. The extent of the injury is not really known to those not with the team, but the hope was that with treatment and rest Carlos would be ready to take the mound soon.
When Martínez will return is still a bit unknown, but apparently when he does, it will be in a relief role. Per Mark Saxon of The Athletic:
Carlos Martinez will pitch in relief when he comes off IL, Mike Shildt said.