Stephen Strasburg diagnosed with left trapezius strain

Tests confirmed that Stephen Strasburg is suffering from a strained left trapezius muscle, according to Nationals manager Matt Williams.

"It's tight, and they're working on it," Williams said. "Of course, it affects his neck and his upper back. So just getting that calmed down as we go along here and then get him back to throwing at some point."

The neck tightness forced Strasburg out of his last start one batter into the second inning, after throwing just 16 pitches. Strasburg told reporters following Friday's game in Cincinnati that he didn't experience the discomfort until he reached the dugout after first inning.

"It doesn't allow him to go out and pitch the way he wants to," Williams said. "The most important thing is that he's not able to go do what he wants to do out there. So we have to get that right and allow him to do that so he can be competitive and pitch the way he wants to pitch and help us win games."

Williams indicated that Strasburg will not begin throwing until the pain completely leaves the irritated area.

"We don't know when that'll be though," Williams said.

Strasburg is experiencing the worst stretch of his six-year career. The right-hander hasn't pitched through the fourth inning in four of his last five starts, with an ERA of 10.13 during the tailspin.

"You talk about Stephen ... he's been pretty darn good since his debut," Williams said. "And this is kind of the first rough patch that he's faced. So we have to make sure that we determine what it is and fix it. And whatever is causing that in his back, we have to fix it. Then get him back out there and allow him to be free and pitch and do what he does best."

Strasburg has not appeared comfortable on the mound throughout the season. Williams has repeatedly asked Strasburg to be more aggressive on the mound, particularly with his once-feared fastball. The idea was raised to Williams that Strasburg's time away from the game may clear up his mental approach.

"It's never good to go on the disabled list," Williams said. "Nobody wants to go there. Does it give him a chance to reset? Yeah, if he's doing what he needs to do to get back to pitch. But for right now, he's idle until that calms down and he can get back to it."