Pena, who remained in the game, fractured a bone in his left hand during last night's game against the Minnesota Twins.
The Royals have called up Luis Hernandez from from Triple-A Omaha.
"He's been hitting pretty good," Royals manager Trey Hillman said before Sunday's game against the Twins. "From my understanding, he's been playing well. He gives us another switch hitter, which never hurts. He's got a little bit of experience."Pena was hitless in his 11 at bats on the season.