Martinez was recalled from Triple-A Round Rock on Wednesday.
Martinez takes the roster spot of starter Lucas Harrell, who was placed on the 15-day DL on Wednesday with a groin strain. It's possible that Martinez will simply slot into the rotation, or the Rangers could opt to go with a four-man rotation and bring Derek Holland off the DL when they next need a fifth starter on Aug. 27. Martinez has been quite good of late at Triple-A (3.23 ERA, 56 strikeouts in last 61.1 innings), but his 7.18 ERA in the big leagues speaks to his inability to get big leaguers out.