MINNEAPOLIS -- Catcher Joe Mauer was held out of the starting lineup on Wednesday against the Rays after taking a foul tip to his right shoulder the night before, but he is expected to return Thursday in Chicago -- where he will play first base for the first time in his big league career.

Mauer, who has been taking ground balls at first base during batting practice since June 27, hasn't played the position since appearing in one game there with Class A Fort Myers in 2003.

"He's been taking plenty of ground balls, and we want Jim Thome in the lineup over there with [Drew] Butera going to catch [Carl] Pavano," manager Ron Gardenhire said Wednesday. "So we gave Joe a little bit of a break today -- he got one at-bat -- but he can be off his legs again tomorrow and play first base."

Mauer, who struck out as a pinch-hitter with the bases loaded to end Wednesday's 12-5 loss, is being called to action at first with Justin Morneau out until at least mid-August after undergoing surgery last week to remove a herniated disk fragment from his neck. It will be a change of pace for Mauer, who last saw extended time at first when he played 13 games there with Class A Quad Cities in 2002.

Mauer said he'll use one of Michael Cuddyer's first baseman gloves and admitted "he's a little nervous" about his first game at first in the big leagues.

"I got a couple days of ground balls in, and he asked me to go over there and play first, so that's what I'll do," Mauer said. "I haven't played a game yet, so I don't know [what to expect]. You have to get out there and play, and that's where I'll be [Thursday]."

Gardenhire said he likes what he's seen from Mauer so far, but he hasn't had a chance to work on any game scenarios, as Mauer has only taken ground balls and worked on his footwork around the bag.

"He's fine," Gardenhire said. "But you won't really know until you get him into a game. He's pretty fluid over there, to tell you the truth. He has soft hands and moves around pretty good. All the fundamental parts of it will be a learning experience for him."

With Mauer out of the lineup on Wednesday, Rene Rivera started behind the plate and caught Francisco Liriano, who struggled and allowed five runs over just 4 1/3 innings.

Mauer admitted this season "will be a grind," and indicated he's still feeling the effects of the bilateral leg weakness that kept him out of action for two months.

"They feel about ... well, me not playing today probably tells you," Mauer said of his knees. "I want to be in that lineup every day. I understand what it's going to be like the rest of the year."

Baker to skip next start with flexor strain

MINNEAPOLIS -- Right-hander Scott Baker, who left Tuesday's start after just five innings and 62 pitches, was diagnosed with a right flexor muscle strain and will miss his next start against the White Sox on Sunday.

Baker was scheduled to get an MRI exam Wednesday afternoon, but Twins manager Ron Gardenhire said he believes the injury isn't serious. Gardenhire, however, said right-hander Anthony Swarzak will get the start instead of Baker for precautionary reasons, even after Swarzak tossed two scoreless innings in relief in Wednesday's 12-5 loss to the Rays.

"We had him basically going for 40 pitches or so, so he'll be fine," Gardenhire said of Swarzak, who threw 31 pitches. "He'll be going Sunday."

Gardenhire added right-hander Kevin Slowey wasn't a candidate to start that game because he is still getting stretched out with Triple-A Rochester, as he's expected to throw 70-75 pitches in a rehab start on Sunday.

Baker's injury was originally called a mild elbow strain, but it's actually his flexor muscle connecting his forearm to his elbow. But Twins trainer Rick McWane echoed Gardenhire's comments that it's not believed to be anything major.

"It didn't look too bad last night," McWane said. "He came in for treatment this morning and it doesn't look that bad. It's just a little sorer than it would be. It's not too alarming."

McWane also added the injury "has nothing to do" with the offseason surgery Baker had that removed bone chips and spurs from his throwing elbow.

Slumping Capps will get a break as Twins' closer

MINNEAPOLIS -- Twins manager Ron Gardenhire hinted he might give closer Matt Capps a breather from his closing duties after he failed to convert a save in each of his last three opportunities.

After blowing his sixth save overall Saturday night, Capps couldn't finish the ninth inning on Sunday or Tuesday, as left-hander Glen Perkins came on in relief and picked up the first two saves of his career.

Gardenhire reiterated Capps "is going to be fine," but the skipper wants Capps to build his confidence back up, which could mean moving him away from the closer role for a day or two.

"I haven't talked to Cappy yet today, but I'll probably talk to Cappy about it," Gardenhire said. "When we get to the end, we'll maybe give him a bit of a blow here. I know he's frustrated, so we'll see what we can do."

Gardenhire said he could choose his closer Thursday based on matchups, as Perkins and right-hander Joe Nathan remain ninth-inning options.

"We'll just do the best we can at the end with who's up and who they have on the bench," Gardenhire said.

Plouffe excelling since being sent to Minors

MINNEAPOLIS -- Twins manager Ron Gardenhire said he's been closely monitoring Trevor Plouffe, who has been impressive at Triple-A Rochester since being optioned on June 3.

Plouffe hit three homers on Tuesday in a doubleheader and he is hitting .308 with a .385 on-base percentage and .663 slugging percentage with 15 homers in 45 games with the Red Wings this year.

Plouffe, who began the season as a shortstop and started 15 games at that position with the Twins this year, has also been moving around the diamond with Rochester -- playing first base, second base, third base, left field and right field in addition to shortstop.

Plouffe played first base for the first time in his Minor League career in the second game of Tuesday's doubleheader after hitting two homers in the first game. Plouffe had also seen action there in Spring Training games.

"I was the one who called and told them to put him at first base for the second game," Gardenhire said. "I'm looking for all the options, including playing first base. I told them to keep doing it pretty much until we call, so we always take notice of that."

Gardenhire said he'd like to recall Plouffe soon, but added his roster is his problem, as he doesn't want to send down utility infielder Luke Hughes. It's more likely that Gardenhire will find room for Plouffe by optioning one of his backup catchers -- Drew Butera or Rene Rivera.