McCann said the pain is behind his right knee, where the hamstring meets the joint. The injury initially occurred during the Braves' road trip last week, but McCann said he's not sure exactly when.
Saturday was the most McCann had been bothered by the injury. He grounded out in his at-bat in the first inning, then made a swiping attempt to tag Nationals left fielder Steve Lombardozzi as he slid in safely to the plate in the top of the second inning. McCann remained in the game for the final two outs of the inning and his spot in the lineup did not come up in the bottom of the second.
"It's hard to squat and move side to side," McCann said. "It was hard to block balls."
Manager Fredi Gonzalez said he is optimistic McCann will be able to return by Monday or Tuesday, when the Braves play a three-game series against the Marlins.
"Hopefully Monday or Tuesday he can crank it up again," Gonzalez.
McCann was replaced in Saturday's win by backup catcher David Ross in the top of the third. Ross went 1-for-3 and led off the eighth inning with a single that led to the winning run for the Braves.
Teddy Cahill is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.