Gardenhire was standing at first base at Comerica Park before the game when he was struck on the ear by a ball thrown by Twins infielder Alexi Casilla, the Minneapolis Star Tribune reported.
The newspaper said Gardenhire's ear was bleeding and the Twins' skipper was suffering from a headache afterward.
Twins officials indicated he would continue to be monitored by doctors. He remained in the clubhouse to start the game.
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