Harper grounded out on what would prove to be his final at-bat of the game. During that at-bat, however, he checked his swing on one pitch and reacted as if he felt some pain. He didn't run out his grounder -- which is rare for Harper -- and immediately began to speak with manager Davey Johnson and head athletic trainer Lee Kuntz. And when the Nats took the field in the bottom of the sixth, Roger Bernadina had replaced Harper.
It's worth noting that Harper banged into the right-field wall Tuesday night.
Harper, 20, is hitting .337/.427/.705 with six doubles, a triple, nine homers and 18 RBI this season. Needless to say, losing him would be a devastating blow to the Nationals, even if only for a short period of time, considering their current injury issues.
UPDATE: Sure enough, the contact with the wall Tuesday night was to blame. Harper has a bad bruise on his lat (via Amanda Comak) and discomfort is what caused him to leave the game Wednesday. But it's a bruise, so it would be surprising to see him miss more than a game or two.