He is planning to travel with the Nationals to Pittsburgh on Monday night and then do more rehab work under the recommendation of Dr. Timothy Kremchek, the Reds' orthopedist.
Zimmerman hurt his shoulder on May 18 sliding headfirst against the Orioles. He continued to play, but was eventually placed on the disabled list on June 3. There is no timetable as to when he will return to action.
"It feels better today," Zimmerman said. "It's the first day I've really done anything. It feels better than it did before. I think we are going to continue to do this and make sure it's strong enough. I'm really not rushing. It's a promising sign.
"I wouldn't say we are out in the clear [regarding surgery]. I haven't picked up a bat, but I'm optimistic after what I felt today. We'll see what happens."
Meanwhile, right-hander Ryan Wagner had his second simulated game on Monday. He had a tough time throwing strikes because of a blister on his finger, but the good news is that he didn't have problems with his right shoulder, which has kept him out of action for more than a year.
Left-hander Odalis Perez said his left shoulder is feeling better. He was able to play catch from 60 feet without any problems. Perez missed a start on Sunday because of shoulder tendinitis. He is slated to pitch on Friday against the Mariners in Seattle.
"Thursday might be the day where the trainer is going to decide about the next day," Perez said.
First baseman Dmitri Young has recovered from the flu and started against the Giants on Monday.
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.