Sizemore was squaring around to bunt with two on in the fourth inning when Rick Porcello's pitch came high and inside. The ball hit Sizemore, and he was attended to briefly on the field before going to the dugout. Sizemore was awarded first base, and Eric Sogard ran for him and remained in the game at third.
X-rays were negative, and Sizemore is day-to-day.
Sizemore was traded from the Tigers to the A's in May for left-handed reliever David Purcey. He's hitting .247 with four home runs.