Seattle Mariners starting pitcher Luis Castillo exited Sunday’s road game against the St. Louis Cardinals in the fourth inning with a lower left leg injury.

The right-hander allowed five hits, one walk and two runs while striking out three in three-plus innings. Castillo allowed a leadoff single in the fourth to Ivan Herrera and was replaced by right-hander Trent Thornton, who retired the next three batters as the Mariners maintained a 7-2 lead through four innings.

Castillo, 31, entered the game with an 11-12 record, 3.60 ERA, 46 walks and 172 strikeouts in 172 1/3 innings over an American League-leading 29 starts this season. He also led the AL last season with 33 starts for Seattle, and all of the majors in 2021 with 33 starts for the Cincinnati Reds.

Castillo is 73-76 with a 3.55 ERA in 210 career games (all starts) with the Reds (2017-22) and Mariners.