Treinen to start Tuesday, Mattheus optioned (with McLouth update)

We have finally learned who will start Tuesday night (or, shall I say, later on today) for the Nationals. It'll be right-hander Blake Treinen, who will be called up from Triple-A Syracuse. Right-handed reliever Ryan Mattheus will be optioned to Syracuse to make room for Treinen on the roster, manager Matt Williams announced after tonight's 4-0 Nats win, which featured a 3-hour, 17-minute rain delay. This will be Treinen's first major league start. He made a brief stint with the Nats earlier this season, allowing one run on 11 hits in 6 2/3 innings over three appearances. The 25-year-old, who was acquired in the Michael Morse deal in early 2013, struck out seven and walked two in his time with the Nats this season. The Nats also considered going with left-hander Ross Detwiler tomorrow, but Williams said that because Treinen has been working out of the rotation, the Nats felt he was a better fit for the spot-start. Treinen last started a game for Syracuse on Saturday, but he pitched just an inning, essentially making it a side session leading into Tuesday's start against the Dodgers. In Treinen's last legit start, he allowed one run on three hits over four innings last Monday. Treinen will just be up for the spot-start, then will almost certainly be optioned back to the minors to make room on the roster for right-hander Doug Fister. Fister will be activated from the disabled list and make his Nationals debut on Friday against the Athletics. Mattheus made two appearances with the Nats after getting promoted from Syracuse last week. He threw three scoreless innings, allowing three hits with a strikeout and a walk. Meanwhile, Williams said that outfielder Nate McLouth suffered a bruised knee and a cut on his right hand after making this tremendous sliding catch up against the barrier in left field tonight. McLouth had to leave the game after the fantastic eighth-inning catch that retired Dee Gordon, with Kevin Frandsen coming on to play left field. Williams said, however, that McLouth won't need stitches to close the wound on his hand, and he'll apparently be OK after making one of the plays of the year and putting his body at risk in the process.