Zimmermann and the Nationals, who hold a 7 1/2-game lead over the Braves in the National League East, will try to sweep the four-game series from Germano and the Cubs.
Zimmermann had his roughest start of the season last time out, allowing eight runs in 3 2/3 innings against the Cardinals. He had never allowed more than six runs in a start.
In his last three starts, Zimmermann has allowed 15 earned runs in 13 2/3 innings, but he said his shoulder, which bothered him a month ago, is fine.
"I felt the way I normally feel," Zimmermann said after the start. "The offense did a great job. You have to tip your cap to those guys. They give you six runs and you do all you can to keep the team in the game and you can't hold it down. This loss is totally my fault."
Germano allowed five runs in five innings against the Giants in his last start. His ERA over his last three starts (14 2/3 innings) is a whopping 10.43. He took the loss in all three outings.
He has thrown 91-93 pitches in each of his last five starts.
Despite dropping the first three games of the series, the Cubs are 9-8 at Nationals Park since it opened in 2008.
Cubs: Volstad, Wood could make 2013 rotation
Right-hander Chris Volstad and left-hander Travis Wood could be members of the Opening Day rotation in 2013, manager Dale Sveum said Wednesday.
"I don't see why not," Sveum said. "There's going to be a lot of things that happen this winter with the roster, I'm sure. You're talking about guys that can pitch, pitch innings who a lot of teams would like. They're fourth and fifth starters and hopefully trying to get better to get into a bigger role to be starters, too. I definitely think they're in the mix."
Volstad, who allowed five runs on nine hits in five innings in Wednesday's 9-1 loss, went 3-3 with a 3.72 ERA in six starts in August.
"He's come back from a lot of adversity through the first part of the year," Sveum said. "He went down, did his work, got back and he's pitched very well, too. It's hard to find guys that have that kind of adversity and that much of a losing streak, and come back and be the same guy every day without hanging his head."
Wood, 25, is 4-11 with a 4.64 ERA in 120 1/3 innings. He lost all six of his starts in August.
Nationals: Burnett to rest sore elbow
Left-hander Sean Burnett is expected to rest his sore elbow for the next few days. He hopes to start throwing soon and isn't expected to get an MRI.
The soreness has bothered Burnett for about two months. In 61 games, Burnett has a 2.49 ERA. He's allowed five runs in his last 5 1/3 innings.
"I had trouble shutting it down," Burnett said. "I was still having success. I'm not going to look at my teammates in the eye and shut it down when I'm still doing well. It just got to the point in the last week to 10 days, I was probably doing more than I should try to create movement, maybe get the velocity up.
"It wasn't fair to my teammates. There were better options in the bullpen than me at the time. It wasn't right for me to go out there at 80 percent and giving up leads the way I was giving them up."
The Nationals have hit six homers in each of their last two games against the Cubs.