Top Prospects: Nathan Karns, RHP, Nationals

WASHINGTON -- The Nationals placed Ross Detwiler on the 15-day disabled list on Sunday, leaving them in need of a starter for Tuesday's game against the Orioles. After Monday's game, Nationals manager Davey Johnson announced that Nathan Karns, the Nationals' 2012 Minor League Pitcher of the Year and No. 6 prospect, will fill that slot.

"It'll be a good test," Johnson said. "We'll find out [if he's ready]. … First time out in spring, he threw the ball good and then got a little anxious. But he's got a great arm. So he's going to start Tuesday."

Karns, 25, will be making his Major League debut. In nine starts with Double-A Harrisburg this season, he was 4-2 with a 4.60 ERA, including 55 strikeouts, 18 walks and one complete game. He was drafted by the Nationals out of Texas Tech in the 12th round of the 2009 First-Year Player Draft.

Left-hander Xavier Cedeno, who was called up for Monday's game but did not pitch, will return to Triple-A Syracuse to make room for Karns on the Nationals' roster.

Johnson said that Karns has a good fastball and hard breaking ball that's "more of a slurve." Nationals catcher Kurt Suzuki caught Karns in Spring Training and said that he liked what he saw.

"[We'll] try to keep him calm, he'll be a little amped up out there," Suzuki said. "It's his first start, he's going to be nervous. But the more fun he has, I think the better he will be."

Sore left knee keeps Harper from lineup vs. O's

PHI@WSH: Johnson discusses Harper Injury

WASHINGTON -- Nationals outfielder Bryce Harper was held out of the starting lineup Monday against the Orioles as he deals with a sore left knee.

Harper injured the knee on May 13, when he collided with the right-field wall at Dodger Stadium, and aggravated it Sunday after a pair of head-first slides. Johnson said Monday that Harper has bursitis in the knee and likely will miss two games. The 20-year-old slugger was replaced in Monday's starting lineup by Roger Bernadina.

"I think it's just uncomfortable -- it's like an inflammation," Johnson said of Harper's knee. "We just need to let it calm down. It was a little more swollen today. I asked him yesterday if he had a lot of fluid there. He didn't have a lot of fluid yesterday, but he looks like he's got more today."

Nationals team doctor Wiemi Douoguih said that Harper had an MRI in which doctors saw some soft tissue swelling but nothing structurally wrong with the knee. Douoguih said the joint in Harper's knee was not affected, but there is still a risk of re-injury, according to head athletic trainer Lee Kuntz.

"If you bump it, it flares up again," Kuntz said. "You'll see a lot of people do the same thing on their elbow. They bump their elbow, it blows up. So the idea is to get it settled down so we can put it to bed and go from there."

Harper could be slotted into the lineup as the designated hitter when the Nationals' series with the Orioles moves to Baltimore on Wednesday and Thursday, Johnson said.

"DHing would probably be good," Johnson said. "He wouldn't run into walls."

Harper leads the Nationals in batting average (.287) and home runs (12). He banged his knee on the ground while sliding into second and third base in the first inning of Sunday's 6-1 win over the Phillies. Bernadina replaced Harper as a pinch-runner in the seventh inning after Harper drew a walk.

"I wanted to try and stay in there until we got a lead or something like that," Harper said after the game. "We got a five-run lead and I wanted that fourth AB. I swing it pretty well against [Phillies starter Cole] Hamels every time I face him, so I really wanted to stay in there against him. Got that five-run lead and got out of there."

Johnson said Monday that he doesn't think the bursitis could lead to any more serious injuries. Harper will take anti-inflammatory medicine to reduce the swelling. He explained after Sunday's game that it only bothers him when he's running the bases.

"I think sometimes when I get a push off my back side [while batting], it hurts a little bit, but it's more the running part and having that fear of sliding and banging it up," Harper said. "But I don't really play with fear. … I mean, I could rest it for four days, feel better and then go out there and slide and bang it up again, and then back to square one."

Espinosa tests wrist, says it feels better

ATL@WSH: Espinosa takes a pitch off his hand

WASHINGTON -- Nationals second baseman Danny Espinosa tested his right wrist during hitting and fielding practice on Monday morning at Nationals Park, and he said the soreness was down significantly.

Although things went well, Espinosa is hoping that the wrist doesn't swell overnight. If it doesn't, Espinosa is aiming for Wednesday or Thursday to appear in a game.

"Warming up, I wasn't feeling the stiffness or the clicking of my wrist," Espinosa said. "As I kept going, I was being more aggressive with my swing. I wasn't thinking about it. I was able to go loosely and naturally."

Espinosa hurt the wrist on April 14, when he was hit by a pitch thrown by Braves left-hander Paul Maholm.

Espinosa did not report there was a problem with the wrist until the team was in San Francisco last week. He went to Baltimore for X-rays on Friday morning, and that is when he learned about the bone chip in the wrist.

"The bone chip that he has is like a bruise. It's not like a fracture, when you normally think of a broken bone," Dr. Wiemi Douoguih said. "It's something that tells us that there is something wrong, but structurally, everything else is sound in that area." 

In other injury news, Douoguih said Jayson Werth's right hamstring is getting better. The Nationals are hoping that Werth returns to action sometime next week. On Sunday, he ran sprints and strengthened the hamstring. 

"Then again, you can't tell. You have to take it one day at a time," Douoguih said. "Yesterday, he looked good, and then you go to the next phase and hope to get him into some rehab starts the next few days." 

Nats honor veterans on Memorial Day

BAL@WSH: Nats, Orioles honor veterans on Memorial Day

WASHINGTON -- Nationals second baseman Danny Espinosa walked into the clubhouse Monday morning, saw the special Memorial Day jersey hanging at his locker, and flagged down a team employee.

"Hey, I want to order one of these," he said. "This is cool."

The Nationals joined the rest of Major League Baseball in honoring fallen members of the military on Monday by wearing jerseys with hints of camouflage officially licensed by the U.S. Marine Corps. Their hats were also camouflaged.

"I think we should wear them once a homestand," shortstop Ian Desmond said of the uniforms. "I think they're the best unis we got. We have military members here all the time, I think it'd be great to show them our support, like the Padres do, not just on Memorial Day."

Beyond uniforms, the Nationals recognized Memorial Day by distributing American flags to the first 20,000 fans to arrive at Nationals Park. The ceremonial first pitch was thrown by Lieutenant General Michael Ferriter, an intelligence officer with more than 33 years of military experience.

The Nationals also partnered with the Tragedy Assistance Program for Survivors (TAPS), a non-profit that supports family and friends of those who have lost a member of the armed forces. More than 500 tickets were donated to members of the organization and their loved ones.

Nationals outfielder Bryce Harper said Memorial Day is particularly meaningful in a place like Washington, where veterans play such an integral role in the community, and Arlington National Cemetery is just a short drive away. Desmond agreed.

"It's a special time here," Desmond said. "You're driving around and bridges have flags on them, people have flags. I saw the Rolling Thunder yesterday, I thought that was really cool; that was the first time I'd seen that. I think it's pretty cool stuff.

"Obviously this isn't a day for barbecues and baseball games. This is obviously a day for remembering. That kind of gets lost in the shuffle from some people's eyes. There's a lot of people who have sacrificed their lives for us, and we really appreciate that."

Worth noting

• Johnson said he wouldn't shave until the team started hitting, but after three straight games of double-digit hits, he was asked Monday what would qualify as enough hitting to prompt a shave.

"Anything over five [runs] is fine," he said with a smile.

• Nationals hitting coach Rick Eckstein coached first base Monday in place of Tony Tarasco, who was excused from the game because of the birth of his child.

• On Monday, the Nationals secured outright waivers on Yunesky Maya, who was designated for assignment Friday. Maya was assigned to Triple-A Syracuse.