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7/3/2013 8:21 P.M. ET

Ramirez encounters setback in recovery

MINNEAPOLIS -- Outfielder Wilkin Ramirez returned to the Twin Cities for further testing after encountering a setback as he recovers from a concussion.

Ramirez, who sustained the injury running into Josh Willingham in the outfield on May 25, was placed on the concussion disabled list the next day.

He played in three rehab games with Class A Advanced Fort Myers but retriggered concussion-like symptoms while diving for a ball on June 22. He's expected to begin a new rehab assignment as soon as he's declared ready by team doctors.

"He's going through tests again," general manager Terry Ryan said. "He jarred his head when he dove for a ball and got dizzy. We wanted to wait a few extra days, because you don't want a guy to go on an airplane after that. So we got through that, and he got yesterday, and now we'll go through the same process again."

Surgery on Willingham's knee deemed a success

MINNEAPOLIS -- Josh Willingham underwent successful arthroscopic surgery on his left meniscus on Wednesday, the Twins announced. Team physician John Steubs performed the operation.

Willingham, who also has a bone bruise in the knee, is expected to be out four to six weeks, but general manager Terry Ryan doesn't want to put a timetable on his return.

"He had a scope this morning," Ryan said. "Everything went well. They repaired the torn meniscus in the left knee. So we'll go from there. He'll be out for a while. I'm not going to put a timeframe or a limit on it. He's certainly going to extend beyond the 15 days. I'm not sure how far, though."

Willingham, 34, is hitting .224/.356/.398 with 10 homers and 37 RBIs in 70 games after batting .260 with a career-high 35 homers and 110 RBIs last season.

But manager Ron Gardenhire said it's unclear just how much Willingham's knee affected him at the plate. Willingham has maintained that the knee only bothered him while running.

"I think Josh is the only person that can tell you that," Gardenhire said. "We've asked him about it -- 'Is it bothering you when you're swinging?' And he'll say no. But if you're physically not able to turn and spin on your legs, it probably does, but he would never admit to that; he's not an excuse-maker."

Draftee Stewart to make pro debut on Thursday

MINNEAPOLIS -- Right-hander Kohl Stewart, the Twins' first-round pick in this year's First-Year Player Draft, is set to make his professional debut on Thursday in the Gulf Coast League against Rays Minor Leaguers in Fort Myers, Fla. He's expected to throw between 40 and 50 pitches.

Stewart, 18, the No. 4 overall selection, signed with the Twins on June 19 with a $4.544 million bonus.

"I'm not too concerned about anything other than getting his feet wet," general manager Terry Ryan said. "This is just his first outing. [Director of player personnel] Mike Radcliff will be down there to see him, which is good, so we can get an evaluation. The only thing I hope is that he throws the ball over the plate."

Stewart, a two-sport star at St. Pius X High School in Houston, was the top-ranked high school pitching prospect in the country, according to MLB.com.

Young outfielders to play more with Willingham out

MINNEAPOLIS -- With Josh Willingham out of the lineup for the next few weeks, some of the Twins' younger outfielders will see their name in the lineup more often.

Willingham underwent surgery on his left knee on Wednesday and isn't expected to return for four to six weeks. The Twins reinstated center fielder Aaron Hicks from his own rehab assignment on Tuesday when they placed Willingham on the disabled list.

Willingham's absence leaves a hole in left field that lately has been filled by Oswaldo Arcia. With Hicks back in center, Chris Parmelee will see more time in right, and Clete Thomas will fill in as needed.

But no matter where they're standing come game time, each of the four outfielders will be getting more time at the plate.

"We're going to move some guys around," manager Ron Gardenhire said. "As I told the outfielders, we're going to do the best we can to keep everybody swinging. Arcia is going to get plenty of at-bats, Parms is going to get at-bats. We'll use Clete, mix and match as best we possibly can with him. These guys are going to get to play a little bit now and see if they can take advantage of it. We'll see what happens."

Rhett Bollinger is a reporter for MLB.com. Read his blog, Bollinger Beat, and follow him on Twitter @RhettBollinger. This story was not subject to the approval of Major League Baseball or its clubs.