The Braves say Simmons was hurt in Wednesday night's game and is day to day.
Simmons made a strong defensive play in the second inning when he went to his right to field a grounder by Travis d'Arnaud. Simmons slipped but recovered to throw out d'Arnaud from his knees. In the fifth, Simmons was out at the plate when he collided with d'Arnaud and fell to the ground. He remained in the game.
Pena, who played in seven games at shortstop in 2013, made his first start of 2014 and singled in four at-bats.
Information from The Associated Press was used in this report.