Stephen Strasburg left after two innings on Sunday. (Matt Kartozian/USA Today Sports)

PHOENIX — The Washington Nationals, already piecing a roster together these days, might have another injury to deal with now. Stephen Strasburg left Sunday’s start against the Diamondbacks after two laborious but scoreless innings with what he described as “achiness” in his forearm, though admitted the problem was hard to describe.

“We think he’s okay. We just took him out for precaution. He couldn’t get loose. We saw he kept shaking his arm,” Nationals Manager Dusty Baker said. “So we just took him out for precaution. He’s had a little stiffness, couldn’t really get loose even though he was throwing the ball well. So we’ll analyze it when we get back home. He’ll see our doctors, and hopefully we’ll have an answer on Tuesday.”

Strasburg’s velocity was fine. His change-up and curveball broke as usual. He did not allow any runs. But he did not look quite right, falling behind nearly every batter, walking the eighth and ninth hitter in order and three batters in two innings overall.

The 28-year-old showed no major signs of trouble, but was making a fist after many pitches, seemingly pulling back on his follow-through. He never looked comfortable and revealed later he felt the same thing in his last start — in which he went seven innings, allowed one run and struck out 11.

“It’s not like really like intense pain in a specific area it’s just kind of like general tightness. I’m having a tough time to really get loose out there and I think it’s just the all-star break kind of messed it up for me throwing-wise and treatment wise,” Strasburg said. “It is what it is. I think my arm is just kind taking a little while to get back in the swing of things. I pitched through it last game and obviously did well but kind of still lingering there. I’d rather be smart about it.”

Strasburg has a long and varied history of injuries, beginning with Tommy John surgery early in his career, then battling shoulder, upper back and right forearm trouble over the past two seasons. The Nationals have already lost one member of their rotation for the year — right-hander Joe Ross, who underwent Tommy John surgery last week. They can absorb that loss. Another, particularly a long-term one, could change their plans entirely.

For now, Strasburg does not expect to need an MRI exam, nor a stint on the disabled list.

“I think it’s something I can work through,” Strasburg said. “I think that’s kind of why I just want to get [out of there today], not let it get any worse, address it and clear it out in time for my next spot in the rotation.”

Because of the Nationals’ day off Monday, Strasburg will get an extra day of rest between Sunday and his next start, resulting in a half-start’s worth of pitches on his arm across 11 days. He said the condition improved between his last start and this one, but that he still wakes up sore, feels the trouble loosen up as he throws, then feels it again “when I really kind of reach back for it.”

After feeling similar — but not at all identical — stiffness late last season, Strasburg found he had a partial tear of his right pronator tendon and missed the last month and a half of the season, including the playoffs. He also saw back tightness burgeon into month-long disabled list stints in 2015. Strasburg set a stated goal of making it through this season healthy, something he could still do by and large. He hopes Sunday’s short start will help him do that.

“I’ve had so much stuff happen just trying not to be selfish out there. I’m not really helping the team If I’m going out there and continually throwing through these things,” Strasburg said. “I just want to be there at the end, that’s like the ultimate goal this year and if getting pulled after a couple inning today if that’s going to put me in a better position to be there, I’ll take it.”

Enny Romero also left Sunday’s game unexpectedly. He had pitched 1 2/3 scoreless innings before walking Paul Goldschmidt, after which he departed with trainer Paul Lessard for what appeared to be an acute and immediate problem.

Romero revealed later that his back tightened up — a “back spasm,” Baker called it. Romero said he experienced similar trouble last season in Tampa Bay, where he landed on the disabled list with what was officially called “a back strain.” Romero said the trouble began in the Goldschmidt at-bat, and prevented him from continuing, though he does not expect to need a disabled list stint this time.

“I think maybe rest tomorrow, and I want to see Tuesday,” Romero said. “I want to throw first and talk to [the trainers].”

More Nationals:

Andrew Stevenson gets his first big league call-up

Roark looks like his old self as the Nationals beat the Diamondbacks

Grace emerges as reliable relief option | Kelley throws 30 pitches in ’pen

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