Strasburg, on the disabled list since May 30, threw for the second time in two weeks. The right-hander was examined June 1 by team doctors in Washington and diagnosed with a strained left trapezius, an upper back muscle where the arm meets the neck.
The 26-year-old, who has limped to a 3-5 record and a 6.55 ERA in 10 starts this season, reported no issues after a session that spanned 60 pitches, Nationals manager Matt Williams said.
"Felt good coming out," Williams said, according to the Washington Post. "We'll re-evaluate him [Saturday]. He's still hot if you will. ... Once he gets a night's sleep and gets back here [Saturday] and we see how he feels, then we'll make another plan from there. No issues throwing today. That's a positive sign."
Strasburg has used his time on the disabled list working with pitching coach Steve McCatty on refining his mechanics and getting consistency with his landing spot. Friday's session bore noticeable improvement.
"It was better on line today," Williams said. "The good thing that he's gone through this is that he's continued to throw and continued to work on his mechanics. Today it was much better and more on line. He was able to put the ball where he wanted to. Good breaking balls, good changeups, good sliders. And the fastball was good. A really good positive sign for us."
Strasburg left his May 29 start against the Cincinnati Reds after just 16 pitches because of neck stiffness, the latest trial in a turbulent 2015 for the 2012 All-Star.
On June 3, Strasburg threw on the flat ground in the outfield of Nationals Park, one day after Williams said Strasburg would not throw until he "feels good." Strasburg emerged without discomfort, Williams said before that day's game against Toronto.
Strasburg will be re-evaluated Saturday to determine the next step in his rehab plan.