Needing a starter for Thursday's game in Pittsburgh, the Nationals have called up right-hander Blake Treinen from Triple-A Syracuse and optioned reliever Ryan Mattheus back down to make room.
Treinen will now take Gio Gonzalez' spot in the Nats' rotation as the lefty serves a 15-day stint on the disabled list with shoulder inflammation.
"Ryan Mattheus, he'll go back to Syracuse," manager Matt Williams said. "He pitched really well, but we have to get Blake here to start."
Treinen, a 25-year-old rookie, will join the Nationals for the third time this season. Through four appearances he holds a 0.77 ERA across 14 2/3 innings.
Treinen last appeared with the Nationals on May 6 in a game against the Los Angeles Dodgers. He made a spot start opposite former Cy Young-winner Clayton Kershaw, and pitched very well. The right-hander went five innings on a pitch count with zero earned runs and seven hits allowed.
Aside from his time with the Nats this season, Treinen has held a 1.96 ERA with Syracuse through six starts. He last pitched on May 16 and allowed two runs through 5 2/3 against the Toledo Mud Hens.
Mattheus leaves the Nats after his first stint with the team this year. He pitched four scoreless outings for a total of 5 2/3 innings.
Gonzalez will test his shoulder on Friday in Pittsburgh and from there hopefully have a timeline to return. It is not clear yet whether Treinen will remain in the rotation after starting on Thursday.