Perez will undergo an MRI on Saturday to examine his right side and rib area, Jeffrey Flanagan of MLB.com reports.

Manager Ned Yost said that he was concerned about the situation. If Perez is found to have an oblique strain or a similar injury, he could easily miss multiple weeks, something the Royals certainly can't afford if they want to make a serious run at the postseason. Drew Butera replaced Perez behind the dish Friday.