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9/19/2013 10:41 P.M. ET

GM encouraged by Mauer's progress from concussion

OAKLAND -- Twins general manager Terry Ryan was happy to report prior to Thursday's series opener against the A's that catcher Joe Mauer has responded positively to treatment with his concussion and that he could rejoin the team upon its return to Minnesota on Monday.

"Slowly but surely he's getting better, and today was one of the better days," Ryan said. "That's better than what I've been telling you. He's making some progress."

It's been exactly a month since Mauer suffered a concussion off a foul tip on Aug. 19. He's been working out at home but is expected to return to Target Field on Friday as he continues to progress. Both the length and intensity of his workouts have increased, Ryan said, and his symptoms have lessened.

"If he continues to have no symptoms, you'll see him," Ryan said. "I'm holding out hope that we ultimately can get him back on the field. So we're working toward that."

Twins trainer Dave Pruemer recommended Mauer work out at home instead of at Target Field, which he's done the past handful of days, though Ryan made a point of saying that the opportunities to exercise are available at Mauer's home.

Minnesota's All-Star catcher, who 's batting .324 with an .880 OPS, 11 home runs and 47 RBIs in 113 games this season, has not had an impact test in a week.

"It's nice to hear that he's feeling better," manager Ron Gardenhire said. "We were at home and he definitely wasn't feeling good when we left. He went through some good times and we know there's going to be some steps backward. Just to hear that he's had a couple good days in a row is a good thing.

"As long as he can come to the ballpark and hang out, that'll be good enough for us. Hopefully we can get him back on the field, but the big thing is his health. Just get him healthy. That's what we're after."

De Vries returns to rotation for road finale

OAKLAND -- Perhaps the circumstances aren't as ideal as manager Ron Gardenhire would've liked, but Cole De Vries was named Minnesota's starter for Sunday's series finale against the A's -- the Twins' final road game of the year.

De Vries was set to be a part of Minnesota's rotation to open the year but has battled through a right forearm strain. He replaces Liam Hendriks, who turned in the worst outing by a Twins pitcher this season in his last outing, giving up seven runs in the first inning of a 12-1 loss to the White Sox on Monday.

Hendriks recorded just two outs against five hits and three walks while throwing 41 pitches. It marked the first time the Twins gave up seven runs in a first inning since July 28, 1997, against the Royals.

"The whole reason to start Cole is somebody had to do bad, and I'm not really excited about the guy who did bad," Gardenhire said. "It'll be nice to see Cole go out there and take the mound again. He pitched pretty well for us last year in some big games against some good teams.

"It'll be interesting to see how he does out there as a starter and gets through this thing, but on the flipside of it, I was hoping that Hendricks would take off and show us a little something. It didn't work out, so we'll make that adjustment right now, but there's a good chance there might be more adjustments as we go along."

De Vries posted a 4.11 ERA in 17 appearances (16 starts) with the Twins last year. He has yet to start in 2013 and has pitched in just two games with the Twins. He was 4-6 with a 4.96 ERA in the Minor Leagues this year.

"With what he had done the year before, you'd hope that he'd take off and see what he could do anyway," Gardenhire said. "He knows how to change speeds and move ball in and out. We wanted to see that. He was doing well in the job, but then injuries happened. If he wants to start, he's going to get his opportunity."

Plouffe swinging hot bat in September

OAKLAND -- The Twins have seen a bump in production from Trevor Plouffe of late. The third baseman has recorded a hit in 12 of 17 September games and reached base safely in eight of his past 17 plate appearances entering Thursday's action.

Plouffe has eight multihit games in September, and he's been held hitless in just seven of 30 games since Aug. 18. His 24 hits in this final month of the regular season rank second in the American League behind Jose Altuve, who had 30.

"He's covering the field," Twins manager Ron Gardenhire said. "You see him shooting balls to right field and pulling the balls he's supposed to. Confidence snowballs, and you feel confident and the ball looks bigger than it normally does, and right now, it looks like he's seeing it pretty well."

Jeff Kirshman is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.