Max Scherzer has been scratched from a scheduled start Friday at Minnesota.
The 16-game winner isn't sure he'll be back in the rotation until a possible playoff appearance.
The Tigers, who entered play Thursday with a one-game lead in the American League Central, named Drew Smyly as the probable starter against the Twins.
Scherzer threw 86 pitches in five innings Sunday against the Twins and said after the game he was fine. On Tuesday during a bullpen session, Scherzer apparently strained his deltoid muscle -- the same spot that caused the Tigers to hold him out of a previous start.
Scherzer said he plans to travel with the team but the shoulder inflammation could make him a spectator for the rest of the regular season.