He has played catch three consecutive days and will have a bullpen session on Saturday in Pittsburgh.
The Nationals have not given a timetable on when Zimmermann will return to Major League action. The team may hold him back for a while, so he could pitch into late September or early October.
"We are going to have his innings limited, so I would like to see him pitch into late September," interim manager Jim Riggleman said. "We may stretch it out a little bit [before he comes back]. Let him get a couple more [bullpen] sessions, simulated games, whatever the case may be. But, physically, I think he is able to go do it."
Zimmermann picked the wrong time to get hurt. He is from Auburndale, Wis., which is two hours away from Milwaukee. He had family and friends at Miller Park this week.
"It's fun to come back to your home state and meet everyone," Zimmermann said. "[It's too bad] I'm not able to pitch, but it's nice to be back."
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.