Gardenhire was taking throws from his middle infielders when he was struck in the right ear by a throw from Alexi Casilla.
"I was throwing a ball home, and Lexi didn't realize that I had turned, and he caught me right in the side of the head," said Gardenhire, who watched the 11-10, 13-inning defeat from the clubhouse. "It hurts quite a bit. I really got smacked."
Gardenhire had blood drained from his ear during the game, but was well enough to spend a short period in the tunnel behind the dugout.
"I went down there for a few minutes, just to get out of the clubhouse, but once the pain meds started to wear off, my head felt like it was on fire," he said.
Gardenhire passed a concussion test and said he expects to manage Sunday's series finale.