Royals manager Ned Yost says Friday he's optimistic Herrera could pitch in Game 3 at Kansas City on Sunday.
Herrera threw just five pitches in the seventh inning of Game 1 before leaving with tightness in his forearm. Yost says an MRI exam was encouraging, but revealed the strain.
The 24-year-old Dominican reliever with a 100 mph fastball was the seventh-inning specialist in the Royals' dominant bullpen this season. He went 4-3 with a 1.41 ERA in 70 appearances, striking out 59 in 70 innings.
Kansas City won the series opener 3-2 in 11 innings.