WASHINGTON — Rookie sensation Stephen Strasburg was scratched from his scheduled start for the Washington Nationals on Tuesday night because he had problems warming up his prized and powerful right arm before the game against the Atlanta Braves.

"Stephen was having trouble getting loose in the bullpen, and so I pulled the plug on it," Nationals general manager Mike Rizzo said, adding that he considered it a "precautionary move."

"There's no shooting pains or anything like that in his shoulder or elbow," Rizzo said.

Strasburg was being examined Tuesday by a team doctor and "appropriate tests will be taken after that," including possibly an MRI or X-ray, the GM said, listing the Nationals' top pitcher's status as day to day. In nine starts for Washington, Strasburg is 5-2 with a 2.32 ERA, 75 strikeouts and 15 walks in 54 1-3 innings. He has won his past three starts.

Word of Strasburg's difficulty was relayed from pitching coach Steve McCatty to Rizzo by a team trainer, and shortly before the scheduled beginning of Tuesday's game, the Nationals PR staff announced that Strasburg would be replaced on the mound by Miguel Batista.

There were scattered boos when that news was delivered via the loudspeakers to fans at Nationals Park — many of whom surely purchased tickets precisely in order to watch Strasburg throw his 100 mph fastballs and hitter-confounding breaking balls. There were more and louder boos before the third inning, when a picture of Strasburg was put on the scoreboard, alongside a written explanation of why he was sitting out.

"Erring on the side of caution," Rizzo said, "I just didn't want him to go out there when he was struggling to get loose."

The Nationals have been quite careful in the way they have brought along Strasburg since choosing him with the No. 1 overall pick in the June 2009 amateur draft, then giving him a record $15.1 million contract right before the August 2009 deadline for getting deals done.

Even though Strasburg was dominant at times during spring training, he was moved to minor league camp in Florida, then began the season at Double-A Harrisburg. The righty was promoted to Triple-A Syracuse in early May, before making his much-anticipated major league debut June 8 — and, somehow, surpassing the hype by striking out 14 batters in a 5-2 victory over the Pittsburgh Pirates.

He left that game after seven innings, part of the pattern of easing him into the rigors of the major leagues. The Nationals have said they would end Strasburg's season when he reaches 160 innings, even if that cap were to come in late August or early September.

So far in 2010, he's thrown 109 2-3 innings total, including in the minors, which essentially matches his count in his final college season at San Diego State: 109 innings.

"We're going to use common sense and be cautious like we have," Rizzo said. "This is a workload that he's never seen before."

The GM said Strasburg, who turned 22 on July 20, showed no signs of any issues during the time since his last start, a 7-3 victory at Cincinnati last Wednesday. Rizzo said the pitcher was fine while throwing a side session and a "clean" bullpen session, then playing catch Monday.