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8/30/2013 11:44 P.M. ET

Nationals contemplating September callups

WASHINGTON -- Manager Davey Johnson did not reveal which Minor League players will join the team when rosters expand on Sunday, but he did give some clues.

Johnson said Friday that the team will call up three pitchers and four or five position players, adding that the pitchers will likely join the Nationals before the position players.

While the callups have not been finalized, a source said that Danny Espinosa will likely not be among them. The source also said that Triple-A shortstop Zach Walters will be called up.

When asked about Walters, who is the Nationals' No. 12 prospect and leads the International League with 29 home runs, Johnson chose his words carefully.

"He's certainly deserving, let's put it that way," Johnson said. "And I would like to see him come up."

Johnson said that each of the callups have played for him before, either with the Nationals or during Spring Training. He only confirmed that one player will definitely rejoin the team: left-hander Ian Krol.

Outfielders Corey Brown and Jeff Kobernus and left-handed reliever Xavier Cedeno are also safe bets to be called up.

Ohlendorf officially tabbed to start Sunday night

WASHINGTON -- Manager Davey Johnson announced Friday that Ross Ohlendorf will start Sunday's series finale against the Mets. However, Johnson also said that he would like to see long reliever Tanner Roark start a game before the season is over.

Roark pitched two scoreless innings Thursday night against the Marlins. The 26-year-old has been impressive in his eight appearances with the Nationals so far, sporting a 4-0 record and 0.93 ERA.

"You want to give him the opportunity to see how that plays going forward into next year, if he would be a candidate to start," Johnson said. "You want to have a good lead on as many good young pitchers as you can going forward. We know about [Ross Detwiler], [Taylor] Jordan, but you need to have more than just five. So we want to give him an opportunity to step up."

The Nationals considered starting Stephen Strasburg on Sunday night for the nationally televised series finale against the Mets because he only threw 22 pitches in his previous start before a rain delay ended his night. Instead, Strasburg will make his regularly scheduled start Monday in Philadelphia.

Washington has won eight of its past nine games entering Friday, but Johnson said the team's performance will not affect his approach with the No. 5 spot in the rotation.

"You do what's best for today with an eye on tomorrow," he said. "The eye on tomorrow might mean having one of these young guys not audition, but give them an opportunity to express their talent."

Feeling light-headed, Davey leaves game early

WASHINGTON -- When Jordan Zimmermann left Friday night's game in the eighth inning, he handed the ball to bench coach Randy Knorr. Manager Davey Johnson was nowhere to be found.

Knorr said that Johnson left the dugout in the fourth inning because he felt light-headed. Knorr assumed his duties as manager for the rest of the game.

"Oh, he's fine," Knorr said. "I think he's just coming down with something. He got a little light-headed, so he just went back upstairs. He's fine, though. I think he might be catching a cold or something."

Ian Desmond said that he noticed that Johnson was missing from the dugout, but he was told that the manager was fine and didn't worry about it. Johnson did not speak to the media following Friday's 3-2 loss to the Mets, but he ran into reporters after grabbing a few things from his office.

"I'll survive," he said.

Worth noting

• Johnson said Friday that Detwiler is "real close" to throwing off a mound. The manager would like to see Detwiler throw one inning and take four days of rest before throwing again to test the left-hander's injured back.

• The Gulf Coast League Nationals defeated the GCL Pirates, 6-1, in the first game of the league's postseason tournament on Friday. Drew Ward, the team's third-round pick in this year's First-Year Player Draft, drove in three runs.

The GCL Nationals finished the regular season with a 49-9 record (.845), the highest winning percentage by a domestic-based club at any level.

Tom Schad is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.