Strasburg was placed on the 10-day disabled list Wednesday with an undisclosed issue, Chelsea Janes of The Washington Post reports.
Strasburg returned from an extended absence due to shoulder inflammation and started July 20 against the Braves, giving up six runs on eight hits and two walks over 4.2 innings. He had been listed as the Nationals' probable starter for Thursday's series opener against the Marlins before his name appeared on the MLB.com transactions log with the DL designation. The details behind the surprise return to the DL aren't fully known, but Janes relays that it's expected that Strasburg suffered a setback related to his shoulder. The Nationals haven't named a replacement starter for Thursday's game, but Jamal Collier of MLB.com reports that the team intends to promote Tommy Milone from Triple-A Syracuse to take the hill. Strasburg is eligible to return from the DL on Aug. 1.