With Bryce Harper and Jayson Werth still ailing in an injury-filled season for Washington, the last thing manager Davey Johnson needed was for his ace to get hurt in the Nationals' 3-2 victory over the Atlanta Braves on Friday night.
But Strasburg lasted just two innings before leaving the shortest outing of his career. He will head back to Washington to have his side examined.
"He was complaining of discomfort warming up, and it was more severe than the last time out," Johnson said. "He's a gamer. He wanted to continue. But something like that -- and I saw him wincing with every throw he made -- but I'm not going to take a chance with his arm. That's the main concern."
The victory trimmed Washington's second-place deficit in the NL East to 4 1/2 games behind the Braves,
Atlanta has dropped two of three and four of six.
Strasburg left with a 2-1 lead. He allowed two hits and one run -- a homer by Freddie Freeman -- with no walks and two strikeouts.
"It's something where, the last few starts, I'd feel it warming up and I'd go out there and wouldn't feel anything," Strasburg said. "Tonight it was more the reverse. I started to feel it a little more."
Stammen (3-1) shut down the Braves by striking out three and allowing no baserunners through the sixth.
In the seventh, Tyler Clippard escaped a bases-loaded jam that he created by allowing an RBI single to Freeman that cut the lead to 3-2 and by hitting the next two batters he faced.
Drew Storen pitched a scoreless eighth for the Nationals, and closer Rafael Soriano converted his 15th save in 18 chances by retiring Freeman on a flyout, striking out B.J. Upton and getting Brian McCann to ground out in the ninth.
The Nationals took the lead in the first off Julio Teheran (3-2) when Span led off with a triple and scored on Steve Lombardozzi's sacrifice fly.
Freeman's fifth homer in the second cut the lead to 2-1 in the bottom of the second, but Strasburg struck out Evan Gattis on five pitches before McCann stepped in.
Strasburg was behind two balls, no strikes when he grimaced after throwing a changeup. He flexed his shoulder before throwing the next pitch and soon retired McCann on a groundout. Strasburg then struck out Uggla on five pitches, but his night was over.
"It's just a little tight back there, but it is what it is," Strasburg said. "I've been battling with it a little bit the last few starts. Davey and (trainer) Lee (Kuntz) thought it was a good decision to come out of the game and not let it progress anymore."
Stammen retired all 12 batters he faced. He was replaced by a pinch-hitter in the top of the seventh.
The Nationals took a 3-1 lead in the sixth when Span tripled again and scored on another sacrifice fly by Bernadina.
Teheran's night ended when Anthony Varvaro replaced him with a runner on second. Teheran allowed seven hits, three runs, one walk and a career-high nine strikeouts.
The Nationals have played just 10 games, winning six, with their projected starting lineup.
"We seem to be having all kinds of problems, but we'll get through it," Johnson said. "Hopefully Stras won't miss too much time."
Strasburg's recent numbers, though, have shown no signs of health problems. He began the night 2-1 with 0.96 ERA in his last four starts.
Now the team has to wonder how much time he will miss.
Washington shut down Strasburg on Sept. 7 last season to limit the workload on his surgically repaired arm, keeping him out of the NL playoffs. The top pick in the 2009 amateur draft, he underwent elbow ligament-replacement surgery on Sept. 10, 2010.
"It's kind of hard when you know what you're going to feel after you throw the pitch," he said. "You just kind of go out there and trick your mind, saying it's not going to happen. But it is what it is. I can't do anything about it. Got to take the next step and go back up to D.C. and have them look at it and see what happens."
Harper missed his fifth straight game with left knee bursitis. Johnson said he won't play this weekend. ... Werth is on a rehab assignment and hopes to return on Tuesday. ... Washington has won three straight against Atlanta after dropping nine consecutive to the Braves. ... Freeman's RBI single raised his average with runners in scoring position to .487, best in the NL. ... Braves LF Justin Upton went 0 for 4 with two strikeouts. ... His struggling brother, B.J. Upton, entered the game as a pinch-runner in the seventh, and his average dropped to .145 with 62 strikeouts in 159 at-bats. ... Braves OF Jason Heyward was in the leadoff spot for the second time in his four-year career and for the first time since June 27, 2011. He finished 0 for 4, dropping his average to .146.