McCullers had been placed on the 10-day disabled list Sunday, when the Astros activated newly acquired reliever Roberto Osuna.
McCullers has told Hinch following the fourth inning Saturday that he felt something different in the area around his forearm. McCullers took his at-bat in the top of the fifth, came back out for the bottom half, fired some warm-up pitches and looked into the dugout.
The Astros have been the only team in the majors that has required only five starting pitchers this season. McCullers has a 3.93 ERA through 126 innings this season.
The Astros have four other prominent players on the disabled list, but shortstop Carlos Correa, second baseman Jose Altuve, outfielder George Springer and catcher Brian McCann are all expected to return before the end of the month.