An injury to one of their top trade chips with the non-waiver deadline approaching was the big news on a day when they built an early lead and then came back to beat the Cubs.
Jean Segura hit a solo homer and the go-ahead double, Khris Davis added a three-run shot, and the Brewers rallied for a 6-5 victory over Chicago after Gallardo left with a hamstring problem in the first game of a day-night doubleheader Tuesday.
Gallardo's status is up in the air after he left with tightness in his left hamstring in the fifth inning.
Manager Ron Roenicke said the team will know more after Gallardo is examined by team physician Dr. William Raasch on Wednesday.
"We're not sure as far as length of time," Roenicke said.
Davis' homer in the seventh on the first pitch from reliever James Russell (1-3) wiped out a 5-2 deficit, and Segura capped the four-run rally with an RBI double, giving the Brewers a 6-5 lead.
Milwaukee survived a major scare after Jim Henderson came on in the ninth.
Pinch hitter Dioner Navarro walked with two out and Welington Castillo barely missed a winning homer, driving a 2-0 pitch just foul beyond the left-field wall. He wound up walking before pinch hitter Cody Ransom flied to center, giving Henderson 13 saves in 16 chances.
Segura and Yuniesky Betancourt hit solo homers as Milwaukee built a 2-0 lead, but that unraveled in the fifth.
The Cubs tied season highs with five runs and six hits in the inning, while Gallardo limped off the field with tightness in his left hamstring.
He came up clutching his leg after delivering a 1-2 pitch to Darwin Barney with two out and the bases loaded and immediately left the game.
Gallardo, whose name has come up in trade rumors with Wednesday's non-waiver deadline approaching, allowed three runs and six hits. He first felt pain in the hamstring in the fourth, when he made a diving catch on Villanueva's bunt.
"As soon as I released it it kind of tightened up a little bit," Gallardo said. "Tightened up enough to just, I think. ... After I felt it on that pitch I figured it was going to be a little difficult to stay in there."
"It's heartbreaking," Villanueva said. "It's a heartbreaking loss. It's frustrating."
The loss was the Cubs' second straight after they swept three games at San Francisco over the weekend. And it came with Wednesday's deadline approaching.
Asked about that after the first game, manager Dale Sveum said, "I just got done with the game. I haven't heard anything."
Villanueva, who gave up six hits and four runs in 6 1/3 innings for Chicago, was in line for the win after dropping his previous three starts.
He left to a nice ovation with a three-run lead and runners on first and third after Betancourt singled.
Davis, who came in as part of a double switch for Carlos Gomez in the sixth, lined Russell's first pitch out to right for the tying three-run homer. Segura put the Brewers ahead with a double after Norichika Aoki singled with two out and stole second and third.
"I was just looking for a good pitch to get that run in and just a little something would have helped the team out. Little," Davis said. "And it ended up being bigger than it was."
Although Jeff Samardzija's name has surfaced in trade rumors, Sveum said he thinks it's "very, very far-fetched" that he gets dealt before Wednesday's deadline. Samardzija, 6-9 with a 3.75 ERA, is not scheduled to become a free agent until after 2015. ... RHP Scott Baker (Tommy John surgery) continued to struggle in his fourth minor league rehab start on Monday, giving up three hits and two runs in 3 1/3 innings for Class A Daytona. "I'm not too concerned because we don't have a need right now," Sveum said. ... Roenicke said he didn't expect any deals before the deadline. ... Marco Estrada threw 2 2/3 innings Monday for Milwaukee's Arizona Rookie League team in his first appearance rehabbing from a strained left hamstring suffered June 3. Roenicke said Estrada will pitch Friday, although the location hasn't been determined, and that he'll need a minimum of two more starts before returning. ... RHP Edwin Jackson (6-11, 4.89 ERA) starts Wednesday for the Cubs, and RHP Wily Peralta (7-10, 4.54) pitches for Milwaukee.