Martinez (shoulder) will begin a rehab assignment as a reliever with Low-A Peoria on Sunday, Derrick Goold of the St. Louis Post-Dispatch reports.
Martinez has battled a shoulder strain since the start of camp, an issue he also dealt with in the back half of last season. The length of his absence means his rehab assignment is unlikely to be brief, though he at least won't have to build up to a starting pitcher's workload before being activated. Martinez could eventually return to the starting rotation later in the season.