Scherzer was given a cortisone shot on Tuesday to address inflammation in the bursa sac under his right shoulder blade. Manager Dave Martinez says Scherzer still has to overcome "that last little bit" of discomfort before he can throw a bullpen session and prove he's ready to pitch in a game.
The Nationals listed Scherzer's injury as a mid-back strain when he was placed on the injured list on July 13, a move retroactive to July 10.
Martinez says he has told Scherzer "we don't want to push it." Right-hander Austin Voth is expected to start in Sunday's final game of the four-game series.
Scherzer is 9-5 with a 2.30 ERA.
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