The former AL MVP and three-time batting champion sprained his right thumb and left the Twins' 5-3 win over the Cleveland Indians on Sunday, Minnesota's fifth victory in six games following a five-game losing streak.
"Hopefully I'll be back in there soon," said Mauer, who singled home Minnesota's first run and later walked and scored. "They (trainers) assured me I'm day to day."
The four-time All-Star played only 82 games a year ago because of a leg injury, but has missed only one game this year.
Mauer got hurt while striking out in the seventh inning and was lifted for a pinch hitter in the ninth.
"I fouled a pitch back and felt it," said Mauer, hitting .298 in 52 games. "It was barking pretty good, so I got some ice on it."
Scott Diamond (4-1) cooled off Cleveland bats, allowing three unearned runs and seven hits without a walk over seven innings.
In six starts since being recalled from the minors May 8, he has walked only four.
Matt Capps pitched the ninth for his 12th save in 13 chances as Minnesota, last in the AL Central, took two of three in the series.
"We manufactured some runs, but missed the ball a few times and let them back in the game," Minnesota manager Ron Gardenhire said. "Every time they got close, we were able to score and get that lead back."
Cleveland fell to 2-7 since sweeping three straight at home from Detroit. They dropped to 4-12 overall against lefty starters this year.
"Not a good homestand, especially when you win the first game of both series and you're not able to win another ballgame," Indians manager Manny Acta said. "We continue to struggle as a team."
The Indians begin a nine-game trip Tuesday in Detroit and play 18 of their next 24 games on the road.
"June is going to be a challenge for us," Acta said. "We're going to have to kick it up a notch."
That's particularly true of the starting rotation.
Justin Masterson (2-5) gave up three runs and seven hits over six innings in one of the better outings by a Cleveland starter of late. In their previous eight games, Indians starters went 2-6 with a 9.52 ERA. That included a poor outing by Masterson on Tuesday when he gave up nine hits and all the runs in six innings of an 8-2 loss to Kansas City.
Gardenhire said strong starts of late have helped the Twins.
"It all starts with starting pitching," Gardenhire said. "Diamond did the job. He threw strikes, got ahead in the count and kept attacking the hitters."
Diamond said he felt comfortable changing speeds and tried to throw strikes on either side of the plate.
"I'd rather attack them and give up a hit than walk guys," he said. "I give up a hit, I can get my ground ball and get out of it."
Diamond struck out two and got 13 outs on grounders.
With the Twins leading 2-0, the teams exchanged sacrifice flies in the fourth. Casilla gave the Twins a 3-0 lead in the top half, then Jose Lopez countered for Cleveland. Shelley Duncan's RBI single later in the inning got the Indians within 3-2. Twins shortstop Brian Dozier's second error of the game fueled the rally.
Willingham and Ryan Doumit singled home runs off reliever Nick Hagadone in the seventh. Ben Revere reached on a bunt and stole second. After replacing his belt, broken on the slide into the bag, Revere scored easily on Willingham's single.
"I think we can have three or four guys bunt in a row," Gardenhire said. "That makes it entertaining for the manager, who can just sit and watch them run around for a while."
Twins LHP Glen Perkins worked a scoreless eighth. Minnesota relievers have held Cleveland to a .175 average and one run in 18 innings this year. ... Gardenhire is awaiting tests on RHP Carl Pavano's sore right shoulder. He showed a sheet of paper to reporters, saying it listed his upcoming rotation. It was blank. Gardenhire said RHP Nick Blackburn, out since May 17 with a strained left quad, could be back soon. ... Twins 3B Trevor Plouffe made an error, but went 3 for 4 and is hitting .423 (11 of 26) in his career at Progressive Field. ... The Twins start a three-game series in Kansas City on Monday. ... Acta is hopeful C Carlos Santana, sidelined since May 26 with a concussion, will return Tuesday. ... Indians 1B Matt LaPorta was 1 for 4 in his first game after being recalled from Triple-A Columbus. ... Indians CF Michael Brantley has hit .370 (17 for 46) during a 12-game streak.