WASHINGTON -- Manager Manny Acta said if the Nationals continue to be inconsistent on the field, the team will call up left-hander John Lannan and right-hander Colin Balester, two of the team's top pitching prospects, sometime after the All-Star break and insert them in the starting rotation.

Balester, who was named to the 2007 All-Star Futures Game in San Francisco, is 2-5 with a 3.53 ERA in 15 starts for Double-A Harrisburg. Balester, 21, said recently he has been much more successful this year because he has added a changeup to his repertoire. He said he relied too much on his fastball last season, leading to a combined ERA of 4.72 ERA for Class A Potomac and Harrisburg.

Lannan was promoted from Double-A Harrisburg to Triple-A Columbus on Monday after pitching six shutout innings against Binghamton on June 16. Lannan was a combined 9-2 with a 2.60 ERA in 14 games for Potomac and Harrisburg before the promotion. In fact, Nationals amateur scouting director Dana Brown told general manager Jim Bowden recently that Lannan could pitch in the big leagues right now.

"There is a chance we'll see those guys later on. Jim has indicated that during the second half or by the end of the year, depending on how they develop in the Minor Leagues, we could see some of those guys," Acta said. "We are pretty clear what we are trying to do here. We are trying to develop players for the future. If the second half of the season comes and we are not battling for a playoff spot, why not throw those kids out there and see what they can do?"

If Lannan and Balester are promoted to the Major Leagues, Acta is planning to handle them cautiously as he has done with rookie left-hander Matt Chico. They would not be allowed to throw over 100 pitches per game and would be taken out of games the moment troubles arises. Acta has often said that he wants pitchers like Chico to leave games with a lead or on a positive note.

Escobar to resume running soon: Acta has often talked about how much Escobar is needed off the bench because of his power. But Escobar said the first priority is to get 100 percent healthy. Escobar has not played a game this season because of a separated right shoulder and right ankle injury.

"Right now, the most important thing for me is to get back on the field healthy and be part of this team," Escobar said. "I can only control what I'm capable of doing. And what I'm doing and what I'm capable of doing is work hard to get back on the field."

Escobar currently is in a throwing program and is throwing 120 feet, but he can't do any running for at least another week.

Speigner returns: The Nationals reacquired right-handed pitcher Levale Speigner from the Minnesota Twins in exchange for outfielder Darnell McDonald on Sunday. Following the transaction, the Nationals outrighted Speigner to Triple-A Columbus

Speigner, 26, went 2-3 with an 8.78 ERA in 19 games (six starts) with Washington before being designated for assignment by the Nationals on Tuesday. He posted a 4.41 ERA in 13 relief appearances.

Once he cleared waivers, the Nationals could have offered the former Rule 5 pick back to the Twins for $25,000 or traded for him. The Nationals chose the latter.

McDonald, who signed with the Nationals as a Minor League free agent on Nov. 6, 2006, was hitting .315 with two home runs and 41 RBI in 73 games with Columbus.

Roger Bernadina, 22, was promoted to Columbus to assume the roster spot vacated by McDonald. Bernadina batted .282, posted a .358 on-base percentage and swiped 25 bases with Double-A Harrisburg.

Stat of the day: The Nationals are 14-14 against National League East clubs this season.

Did you know? Nationals bench coach Pat Corrales managed the Indians from 1983-1987. The team's best season under Corrales occurred in 1986, when it went 84-78.

Coming up: The Nationals travel to Atlanta to play a three-game series against the Braves starting Monday night. In Game 1, Washington right-hander Jason Bergmann (1-3, 2.76 ERA) will face Atlanta right-hander Tim Hudson (6-5, 3.43 ERA) in a 7:05 p.m. ET start.