Strasburg looked strong early on, but left in the third. (Greg Fiume/Getty Images)

Stephen Strasburg left Wednesday night’s game after getting one out in the third inning, a troubling turn of events for the right-hander who was activated from the disabled list before the game. Nationals Manager Dusty Baker said Strasburg felt a “pinch in the back of his elbow” and will be undergo an MRI exam Thursday.

“I don’t have much to tell you,” Baker said. “He’s going to get an MRI tomorrow. And we didn’t want to chance taking him any further. He didn’t stick around because he’s just frustrated and upset.”

Strasburg had been on the disabled list with what the team called “right elbow soreness,” a move that seemed largely precautionary as he returned shortly after being eligible to do so. The Nationals analyzed his mechanics, velocity, spin rate and other indicators, and found no signs of major trouble. Strasburg underwent an MRI before he signed his seven-year, $175 millionextension in May, and all was well. But whether because of a new problem or an old one, he experienced discomfort 42 pitches into his return.

“He wasn’t trying to be a hero. He said that he felt fine. But a lot of times you really don’t know until you get into action,” Baker said. “It’s like guys who have pulled hamstrings. They say they’re fine, then they run and jump and everything, and as soon as they get back in action they put a little extra. We thought everything was fine because Ramos said he was throwing the heck out of the ball. He said his change-up was outstanding, and he had good command. And usually if something’s wrong, you don’t have command. So we’re hoping that it’s something minor, but again we’ll find out more tomorrow.”

In the third inning, Strasburg threw a pitch that flew high and away to Braves starter Mike Foltynewicz — significantly wilder than any pitch he had thrown yet. He grimaced afterward and pounded his glove. He threw one more pitch, an inside something at 84 mph, to Foltynewicz, who fouled it off as he tried to bunt. Then Danny Espinosa wandered in from shortstop. Mike Maddux hustled out from the dugout. Trainer Paul Lessard came, too. After a lengthy discussion, Strasburg left the game. He covered his face with his glove as he walked off the mound.

“We simply noticed when he made a gesture on the mound when he threw a pitch high and we saw on his face that his reaction wasn’t very good,” catcher Wilson Ramos said. “And, there, we went to the mound to see what happened.

“His pitches were working very well. His velocity was high,” he continued. “And when he got hurt, I felt bad right away, because we need Stephen in the rotation. He’s helped us a lot and we need him a lot.”

Strasburg had, indeed, looked strong early on, sitting at 96 mph with his fastball and showing as devastating a change-up as he had all season. He struck out four of the seven batters he retired. The Nationals placed him on the disabled list August 21, and he was able to begin throwing bullpen sessions shortly after — something he did every other day for more than a week before returning.

The 28-year-old underwent Tommy John surgery after experiencing pain in his elbow in late August 2010. Pain in the elbow does not necessarily indicate major damage to the ulnar collateral ligament Strasburg had replaced then. It does, however, stoke near-hysteria for any pitcher, because pain in the elbow rarely indicates a minor problem, either.