Zimmerman had been listed as the starter when lineups were posted before the game. But when the players took the field, Mark DeRosa was at third base.
The team said there was no structural damage and listed Zimmerman as day to day.
Zimmerman had fouled a ball off his left foot Friday night against the Marlins but stayed in. Washington manager Davey Johnson said before Saturday's game he planned to give Zimmerman a day off Sunday.