WASHINGTON -- The Nationals are expected make callups on Saturday, and outfielder Eury Perez, catcher Sandy Leon, left-hander John Lannan and right-hander Christian Garcia are expected to be promoted to the big leagues. Once his season is over, outfielder Corey Brown will be called up.

Mark DeRosa will be activated from the disabled list, while right-hander Chien-Ming Wang is expected to make one Minor League start before he is activated from the DL.

Lannan be part of the Nationals' bullpen until it's time to replace Stephen Strasburg in the rotation. In his last two starts, Lannan has pitched two complete-game shutouts for Triple-A Syracuse and has seen his ERA drop to 4.30. Lannan, who was twice Washington's Opening Day starter, has also made two Major League starts this year, defeating the Braves and Marlins.

"It's great. John has had a great attitude down there," manager Davey Johnson said. "He has come up and really been excited about coming up and helping us win. He has done that twice and has thrown great games. I think his arm and his head are in the right place. There is never going to any doubt who is going to replace Stras."

Perez was arguably the team's best prospect in 2012, hitting a combined .314 with 42 RBIs for Gulf Coast Nationals, Double-A Harrisburg and Syracuse. Ranked fifth among Nationals prospects by MLB.com, he will be used as primarily as a pinch-runner.

"Eury's an impressive guy. He's a guy that really came on our radar screen two winters ago in the Winter League when he was Rookie of the Year in that Dominican Winter League," Rizzo said. "He hasn't taken a step backward; he's moving forward, he's developing at a great pace. The player development system has done a great job with him. He's got some exciting skills and a right-handed bat that we view can really help us in the future."

DeRosa has been on the disabled list since Aug. 6 because of a left abdomen strain and is looking to contribute to the team. DeRosa has played in 34 games and is 10-for-66 (.152) with six RBIs. It didn't help that he missed a lot of time during the first half because of a left oblique strain.

"It's huge [to be back]. It has been frustrating the way my year has gone, personally," DeRosa said. "We played so well. These guys have been so great. They kind of let me hang around and give my input and making me feel like I have been a piece in the puzzle. So it's great to come back, just fit in where Davey needs me -- helps us get over the hump. It kind of the situation I've been in all year, trying to get a few knocks."

Garcia, a former Yankees prospect, is a combined 2-0 with a 0.79 ERA and 19 saves in 43 games for Double-A Harrisburg and Triple A Syracuse.

Nats righties Rodriguez, Giolito undergo surgery

WASHINGTON -- Nationals right-handers Henry Rodriguez and Lucas Giolito had arm surgeries performed on Friday.

It turns out that Rodriguez had a loose body removed from the elbow and cannot pick up a ball for at least three months. However, Rodriguez is expected to be ready for Spring Training.

Rodriguez has been on the disabled list since Aug 2 because of another injury -- a lower back strain. Rodriguez had been complaining about the elbow injury two weeks before he went on the DL, according to general manager Mike Rizzo.

"Henry's procedure was similar to the one that Drew Storen had," Rizzo said. "He had the bone fragment, the bone spur removed from his elbow. So they cleaned it up, and he should rehab and be prepared for the beginning of Spring Training."

Rodriguez appeared in 35 games and had a 5.83 ERA with nine saves. He started the season as the closer, but Rodriguez lost the job to Tyler Clippard later in the spring after he was not productive on the mound.

"He was pitching with a lot of pain," Johnson said. "He is big and strong. He just kind of hid [the pain]. He was letter perfect in the spring, he was fresh. ... Then he started having some lulls. From what the doctor said, the elbow was in a lot worse shape than he anticipated. ... [The doctors] had to do more cleanup work than they thought going in."

As for Giolito -- who had been pitching for the Gulf Coast League Nationals -- he had Tommy John surgery performed by Dr. Lewis Yocum in Southern California. His fastball had been clocked as high as 100 mph, and he has a power curveball, but he endured right elbow problems earlier this year, spraining his ulnar collateral ligament.

Giolito would have been a higher pick in this year's First-Year Player Draft if not for the injury.

During the Rizzo era, the Nationals have had their share of pitchers -- Stephen Strasburg and Jordan Zimmermann to name two -- who have had Tommy John surgery and have come back to become successful pitchers.