Update: Nationals trainer Lee Kuntz told the media later it's actually a Grade 1 lat strain, Adam Kilgore of the Washington Post reports.
Strasburg started against the Atlanta Braves on Friday, but only pitched two innings before leaving the game with the injury. The starting pitcher flew back to Washington following the game so team doctors could evaluate him.
Nationals manager Davey Johnson told Jon Cooper of MLB.com that the team will wait to see if they need to put Strasburg on the disabled list. Washington has an off-day on Monday, so they could push the starter back or potentially skip a start. Strasburg had been pitching through the pain earlier this season, so the team is hopeful the injury is minor.
Strasburg is 3-5 on the season, but owns an excellent 2.54 ERA. The right-handed pitcher's strikeouts are down from last season, but he is still fanning 25% of hitters faced, which is 5% better than league-average.