General Manager Mike Rizzo was apparently the one who made the executive decision to scratch Stephen Strasburg for tonight's game against the Braves. Via Mark Zuckerman:
Rizzo pulled the plug after being told #Strasburg was having trouble getting loose in pen. MRI, X-ray planned. At this pt, he's day to day.
It's unclear what was ailing Strasburg. Stay tuned to this stream for updates.