MINNEAPOLIS -- Reigning AL MVP Joe Mauer left Minnesota's game against Oakland on Sunday with a balky left knee and is day to day.
Mauer tweaked the knee while swinging when he grounded out in the sixth. He was replaced defensively by Jose Morales in the seventh.
"I really don't know a whole lot right now," Mauer said. "Obviously I'd rather not have this going on, but here it is."
Mauer said the pain in his knee began to worsen as he ran down the baseline.
"I thought it was the right time to get out of the game," he said.
Mauer had surgery to repair a meniscus tear in the same knee in 2004.
Twins team physician Dr. John Steubs examined the knee on Sunday, The (Minneapolis) Star Tribune reported.
"He said to give it a couple days," Mauer said, according to the report. "That's what we are doing."
The Twins entered Sunday with a 10-game lead in the AL Central, and the playoffs seem all but certain.
"It's frustrating any time," Mauer said. "We're going to see how it is the next couple of days and go from there.
Said manager Ron Gardenhire: "It's one of these day-to-day things. It's not a big deal. At least that's what they're telling me today. There's no fluid, there's no any of that in there. Maybe just a little of inflammation. So we'll [see] how it goes."
Mauer ranks second in the AL with a .331 batting average and is hitting .372 since Aug. 3. He went 1 for 3 against the Athletics.
"He's been battling a little bit of a sore knee here and there anyway, but it's not been a big deal once he gets playing," Gardenhire said. "It's always been fine."
Information from The Associated Press was used in this report.