The decision apparently was made while he was warming up in the team's bullpen just before the game.
Strasburg had a conversation with pitching coach Steve McCatty with Pudge Rodriguez standing beside them with an arm on Strasburg's shoulder.
"I just said, 'Well, how're you feeling?' He said, 'I feel stiff. My shoulder's stiff,' " McCatty recalled hours later Tuesday night.
"I said, 'How bad?' He said, 'It's just stiff, but I can get loose.' I said, 'Uh, no.' And that was it,'' McCatty continued.
MASN said during its broadcast that Strasburg "could not get loose" in the bullpen, so the Nats shut him down as a precaution. Team GM Mike Rizzo confirmed the report during the game. He said Strasburg was "day-to-day."
Strasburg was checked by a team doctor and sent for an MRI and X-ray. Rizzo said none of the tests showed structural problems, and that Strasburg was diagnosed with inflammation in his rather valuable right shoulder.
"No cuff damage. No labral damage,'' Rizzo said, ``so that's good news.''
The team is not certain when the righty will pitch next.
"We're still not sure where he's at,'' the GM said.
There were some boos from the large crowd at Nats Park when it was announced that Strasburg was scratched and Miguel Batista would take his place.
Strasburg was supposed to meet Braves rookie All-Star Jason Heyward for the first time this season. The highly anticipated matchup will have to wait for another opportunity later in the season when the two teams meet again.