Zimmerman, the Nationals' first-round pick in the 2005 First-Year Player Draft, will become the second player in the last three years to be drafted by the Nationals/Expos and be promoted to the Majors in the same season. Closer Chad Cordero was drafted in June 2003 and made it to the big leagues in late August that year.
The organization has already compared Zimmerman to the likes of Hall of Famers Brooks Robinson and Mike Schmidt, along with Arizona's Troy Glaus, and it believes that Zimmerman has the agility to play shortstop, if necessary.
Zimmerman, 20, joins the Nationals after hitting a combined .337 (83-for-246) with 11 home runs and 38 RBIs at Harrisburg and Class A Savannah. Zimmerman, who is from Virginia Beach, Va., has hit more homers with a wood bat (11) as a pro than he did using an aluminum bat (six) during his final season at the University of Virginia.
"He has been very impressive by the way he plays the game," interim general manager Jim Bowden said. "Defensively, he makes plays you don't even think a third baseman makes. He moves runners, he is always scoring a run and driving in a run."
However, fans shouldn't look for Zimmerman to replace Vinny Castilla as the everyday third baseman right away. The Nationals plan to start Zimmerman off slowly.
"It's nice to be able to expose a young future star for a pennant race," Bowden said. "No matter how much he plays, the experience he is about to get here will be invaluable.
"Vinny is our third baseman, and we are trying to win. You have to give people days off. You have to keep people healthy and you have to play the best players to win. It's a big adjustment from college to the big leagues in a couple of months. [Zimmerman] is not here to be a savior."
Zimmerman is the only player from the Nationals' farm system that will be called up on Thursday. Budget restraints prevented them from calling up more players. However, Bowden expects more promotions in another week.
"We are going to make the best moves we can and watch out budget," Bowden said. "The Triple-A team [in New Orleans] plays through Sept. 5. So it may be an advantage to wait a few days, save the money and call up an extra one or two guys rather than call them up right now and limit ourselves."
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.