Zimmerman has been able to jog, but it is going to take some time before he is able to go at full speed. Zimmerman said the hamstring is about 50-to-60-percent healed in terms of trying to run at full speed.
"It's not really the hitting or the throwing or anything like that. It's going to be the running, obviously," Zimmerman said. "The danger of coming back too quick, it's very easy to reinjure [the hamstring]. And then, obviously, I would be definitely done for the year.
"We are kind of at a fine line. Obviously, I want to get back, be out there, help the team and get some games in as quickly as I can. If you rush it too much, you put yourself in a lot of danger of reinjuring it, which no one wants. Running is going to be the biggest test."
Zimmerman also needs to get in game shape. He acknowledges that he gets "fatigued and sore" after practice.
"It's coming along. Everything has been positive and good so far. We're not there yet. We are a little ways away," Zimmerman said.
Once he is ready to play, Zimmerman will start playing in the instructional league at the club's Minor League complex in Viera, Fla., to get at-bats. Once he returns to the Nationals, Zimmerman could see time at third base, first base and left field.
Bill Ladson is a reporter for MLB.com and writes an MLBlog, All Nats All the time. He also could be found on Twitter @WashingNats. This story was not subject to the approval of Major League Baseball or its clubs.