The right-hander carried a two-hitter into the seventh inning, Mat Gamel hit a three-run homer in his first career start and the Brewers completed a three-game sweep of the St. Louis Cardinals with an 8-4 victory Monday night.
"Obviously, it's a huge loss, but to be honest I didn't know until just a few minutes ago," Looper said. "I'm in my own world with the headphones, not really knowing what's going on.
"But you feel for the guy."
Jason Kendall became the eighth full-time catcher to reach 2,000 hits for the Brewers, who have won 12 of 14 overall and 10 of 11 over the Cardinals the last two seasons. They won their sixth in a row hours after learning Weeks will miss the rest of the season with a wrist injury, and are a major league-best 20-5 since a 4-9 start.
"I love Rickie, and I told everybody that," Milwaukee manager Ken Macha said. "He's a tremendous guy but we need to go out and play, too."
Craig Counsell, who replaced Weeks in the leadoff spot and at second base, was 1 for 6.
Kyle Lohse (3-3) struggled with control on two days' rest after working two innings in Friday's rainout, trailing 4-0 after four innings while throwing 89 pitches. Colby Rasmus and Skip Schumaker hit two-run homers in the seventh for St. Louis, which totaled two runs the first two games in the series.
"Everything was up," Lohse said. "About eight at-bats went six pitches or more and anytime you have that, you're working really hard and they're seeing everything you've got.
"You leave one up, and they hit it."
The Cardinals converted Looper (4-2) to a starter in 2007 and he settled for a free-agent deal with Milwaukee after going 12-14 last year. Rasmus' third homer off Looper came after first baseman Prince Fielder's fielding error to start the seventh and represented St. Louis' first earned run off him in 23 career innings over 17 appearances, the first 16 in relief.
Looper, though 62-60 for his career, is the winningest pitcher at 4-year-old Busch Stadium with a 21-13 record and 3.52 ERA.
"You obviously want to win every game, but I have a lot of friends over there and people I've played with for quite a few years," Looper said. "I'd be lying if I didn't say it's a little extra sweet."
Cardinals pitchers combined for 11 walks in the finale, and 23 in the series. Fielder had an RBI single and walked four times for the second time in his career -- the first also came in St. Louis on April 15, 2008.
Looper said umpire Tim Timmons' strike zone was minuscule for both teams, venting his frustration before leaving the mound.
"Luckily we got the four runs," Looper said. "So I just kept trying to throw the ball down the middle, to be honest with you, just to get a strike."
Gamel was recalled from Triple-A Nashville on Thursday. He had one at-bat this season before getting the start at third base ahead of Bill Hall, 1 for 15 against Lohse. Gamel homered into the Cardinals' bullpen in right on a 1-2 pitch to cap a four-run third.
Kendall singled up the middle off Lohse with one out in the second for his milestone hit and added an RBI single in the fifth for his second straight two-hit game. He is 47 hits behind Johnny Bench for seventh on the list among players with at least 1,000 games as a catcher.
Lohse has allowed 17 runs in 14 1/3 innings his last three starts after going 3-0 with a 1.97 ERA in April.
The Cardinals started three rookie OFs -- Nick Stavinoha in LF, Rasmus in CF and Shane Robinson in RF -- for the first time since Sept. 25, 1996, against the Pirates, according to the Elias Sports Bureau. Manager Tony La Russa used Terry Bradshaw in LF, Miguel Mejia in CF and Mark Sweeney in RF in the '96 game. ... Khalil Greene struck out as a pinch hitter in the eighth and is in a 2-for-23 slump.