The Rangers said the injury is not considered to be serious. Darvish, who was receiving treatment after exiting the game, is expected to make his next start Saturday against the Oakland A's.
Darvish allowed back-to-back doubles to Marlon Byrd and Pedro Alvarez with two outs in the top of the seventh to fall behind 1-0. Darvish made one of his most efficient starts of the season, needing only 81 pitches to get through seven innings.
Darvish left a start on Aug. 24 at Chicago because of the same cramping issues in his lower left leg. He also went seven innings in that start.
He came back on Aug. 30 and pitched at home against Minnesota and took a no-hitter into the seventh inning before allowing two home runs and losing to the Twins 3-2.