WASHINGTON -- The Nationals placed right-hander Jason Marquis on the 15-day disabled list Wednesday with bone chips in his right elbow.

The team will recall right-hander Luis Atilano from Triple-A Syracuse after Thursday's game, and he will make his Major League debut against the Dodgers the following day at Nationals Park.

The news comes three days after Marquis became the first starter in Nationals history to not record an out in a game. Marquis threw 28 pitches, 13 strikes, in that tough start, and he has given up 19 earned runs in 8 1/3 innings for Washington this season.

"It's hard to pitch with [bone chips] in the elbow," said general manager Mike Rizzo. "He was probably trying to gut it out. In my opinion, [the injury] probably has something to do with his poor performance."

After Sunday's game, Marquis insisted that he wasn't injured. Even manager Jim Riggleman wondered if something was wrong.

"It's an embarrassment, what I'm doing out there right now," Marquis said on Sunday. "I have to find that answer quick. It's just not happening right now. I don't think there is anything behind the ball. I don't feel any power, any feel of a release point to get the ball where I want it right now. I have to find a way to get it done. I don't think my delivery is where I want it to be. I have no excuses. I just want to get it done. That's all it comes down to."

Marquis threw bullpen sessions the two days following his previous start, but his elbow became stiff by Tuesday night. Marquis informed the team Wednesday morning and had an MRI and an arthrogram. Marquis will see Dr. Tim Kremchek, the Reds' medical director, for a second opinion.

"The trainer took a look at it and called our team doctor, and we got him in to get an MRI," Rizzo said. "It showed there are some floating bodies in the elbow. We are going to get a second opinion."

Atilano, 24, has pitched in two games for Triple-A Syracuse, and has given up two runs in 11 innings for the Chiefs. He was acquired from the Braves in 2006 for first baseman Daryle Ward. At the time of the trade, Atilano was recovering from elbow reconstruction, but he went a combined 9-8 with a 4.01 ERA for Double-A Harrisburg and Triple-A Syracuse last season.

Zimmerman exits with hamstring cramps

WASHINGTON -- Nationals third baseman Ryan Zimmerman left Wednesday's 6-4 victory over the Rockies with cramping in his right hamstring.

With two outs in the seventh inning, Zimmerman hit the ball over the head of right fielder Brad Hawpe, and he was in pain as he reached second base. Zimmerman left the game minutes later with the score tied at 4.

Zimmerman missed a few games last week because of a left hamstring strain.

"It didn't feel like the other one," Zimmerman said after the game. "It felt like cramps more than anything. It's frustrating. We are playing well, and I'm seeing the ball well. It's the last thing I want to happen."

Zimmerman said he is not sure if he will play Thursday afternoon against the Rockies.

"It doesn't feel as bad as the other one," he said. "We'll see how it feels in the morning. We'll lean toward the precautionary side, as we did with the other one."

Zimmerman is hitting .341 with two home runs and 10 RBIs on the season.

Guzman getting significant playing time

WASHINGTON -- Cristian Guzman, who lost his starting job to shortstop Ian Desmond to start the season, continues to find a way to get playing time. Entering Wednesday's action, Guzman was tied with Nyjer Morgan for the team lead in at-bats with 47 and is second on the team with a .362 batting average.

Manager Jim Riggleman gave Guzman a start at shortstop Wednesday, but the skipper insisted that he is still going with a rotation of Guzman, Desmond and second baseman Adam Kennedy up the middle, not with the hot hand. Guzman had four hits in Tuesday's game against the Rockies.

"I'm just trying [to give] all three of those guys playing [time]," Riggleman said. "All three guys are playing so well that I'm not going to let any of them sit three days and not play. They are playing so good that I keep them all in there as much as I can."

Desmond and Kennedy are playing great defensively, but they are hitting .256 and .257, respectively.

Slugger Dunn fighting through slump

WASHINGTON -- Manager Jim Riggleman had a meeting with hitting coach Rick Eckstein and wanted to know what's wrong with first baseman Adam Dunn at the plate. Entering Wednesday's action, Dunn is hitting .163 with a home run and two RBIs.

Eckstein told the skipper that Dunn is swinging late at the fastball and swinging too early at breaking pitches. Eckstein believes Dunn needs to have a better game plan.

"We are trying to work with him and his plan and executing that plan," Eckstein said. "He is a feel guy, and the feeling isn't quite there. He is showing better signs the last several days. It's a work in progress."

Pudge to catch Hernandez's start

WASHINGTON -- Catcher Ivan Rodriguez was planning to start the first three games against the Rockies and then take the day off on Thursday afternoon, but after learning that right-hander Livan Hernandez was pitching Thursday, Rodriguez asked to take Wednesday off instead. Manager Jim Riggleman agreed.

Rodriguez was behind the plate Saturday, when Hernandez pitched a shutout against the Brewers at Nationals Park.