Gonzalez headed to DL for first time in his career (updated after MRI)

Remember last night, when Matt Williams said there was nothing physically wrong with left-hander Gio Gonzalez, who sounded as if he was contradicting his manager by saying he just had to pitch through an unspecified issue?

Well, chalk one up for Gonzalez, who this morning was placed on the 15-day disabled list for the first time in his career. The problem: left shoulder inflammation.

Since joining the Nats in 2012, Gonzalez's 35 victories are tied for the most in the majors by a southpaw with the Angels' C.J. Wilson. But Gonzalez is only 3-4 with a 4.62 ERA this season, and took the loss Saturday night and lasted just three innings. He's lost all three of his May starts.

To replace Gonzalez on the 25-man roster, the Nationals recalled right-hander Ryan Mattheus from Triple-A Syracuse, where he had two saves and a 5.93 ERA in 13 outings. But Mattheus' stay could be temporary, as the Nats bolster their bullpen until Thursday, when Gonzalez's next turn in the rotation rolls around.

Blake Treinen started two days ago for Syracuse, and would seem to be the logical choice to make Thursday's start.

Nationals general manager Mike Rizzo is expected to address the media at noon to talk about today's transactions.

Update: Rizzo just finished addressing reporters and said that Gonzalez, who was pushed back a day from a scheduled start a month ago, complained yesterday of soreness and said his shoulder was "barking." Team doctors performed a strength assessment, which Rizzo said Gonzalez passed, but more diagnostic tests were ordered.

That Nationals sent the lefty for an MRI, and as part of that procedure, Gonzalez will have dye injected into his shoulder so physicians can more clearly see what's causing the problem in his pitching shoulder.

"We put him on the DL because he's having an MRI arthogram," Rizzo said. "When you inject the dye, it's a five-day no-throw program once you get the dye put in. So we just figured he'll miss two starts and we'll find out what's going on in there."

Rizzo sounded as confounded as anyone about what's wrong with Gonzalez.

"I thought he looked fine," the GM said of Saturday's three-inning start. "His arm speed was good. His rotation rates, his spin rate, was fine - good as it's always been on his breaking ball, and his fastball velocity was good. The command part of it, which sometimes comes and goes with Gio anyway, was something that was causing him an issue."

But Rizzo expressed concern that Gonzalez is worried something is wrong, even if he didn't sound particularly concerned, pending results of the MRI.

"We're going to take our time with him and be careful with him because he's vital to our ballclub," Rizzo said.

Update II: In his postgame press conference, Williams said the MRI performed this afternoon on Gonzalez's left shoulder showed only inflammation, no structural damage. That's good news for the Nationals.

Gonzalez will now rest for four to five days in hopes that the inflammation will calm down.