MINNEAPOLIS -- Byron Buxton will begin a rehab assignment with Class A Cedar Rapids on Sunday and could return to the Twins during the club's upcoming road trip that begins on Tuesday in Chicago.

The current plan is for Buxton to start at designated hitter on Sunday and play in the field on Monday for the Kernels against Peoria before the Twins evaluate the center fielder's condition and determine when he could return.

"It's definitely exciting," manager Rocco Baldelli said. "I think we're happy to see Buck finally getting back out there. The rehab went great. He healed up well. Obviously not completely out of the woods yet because we want to see him get out there, run around and be able to take part in game action and everything that entails."

Buxton has been on the injured list since Aug. 3 with a left shoulder subluxation (partial dislocation) that was sustained on a collision with the outfield wall at Marlins Park. He had missed 10 games in late July with concussion-like symptoms after a diving catch in the outfield.

Rosario out of lineup for second consecutive game

Eddie Rosario worked out on the field and took batting practice again on Saturday, but he was out of the starting lineup for a second straight game. He was removed from Thursday's series finale against the White Sox as a precaution for a right hamstring strain.

Baldelli expected to have a better sense for whether or not the left fielder might need a stint on the injured list sometime Saturday or Sunday.

"This isn't some sort of major hamstring issue or injury," Baldelli said. "But that being said, if it's going to take him six, seven, eight days for him to get back to where he might be ready to play, then we have to talk about what's next."

Harper optioned; Stashak recalled

Ryne Harper was optioned to Triple-A Rochester on Saturday after allowing two earned runs on three hits in 1 1/3 innings during the Twins' loss to the Tigers on Friday night. In a corresponding move, Cody Stashak was recalled from the Red Wings.

It marked the first time this season Harper was optioned after the 30-year-old rookie was a surprise addition to the Opening Day roster following a successful Spring Training. The curveball specialist has a 3.65 ERA with 45 strikeouts and nine walks in a team-leading 56 appearances this season.

"We're also in a spot where we have a seven-man bullpen right now, too," Baldelli said. "It's almost impossible for an optionable reliever, a guy with options, to not spend some time at the Triple-A level when you do have a seven-man 'pen. This just happened to be that time."

Harper posted a 1.61 ERA through the end of May but has been more hittable since the All-Star break. Opposing hitters have slashed .333/.340/.549 against the right-hander in the second half, leading to a 5.84 ERA in that span.

"When you're in the first time around in Major League Baseball, you're facing good hitters," Baldelli said. "But if they don't know you, you can do whatever it is you want to do. But as time goes on, you have to make adjustments, too, like everyone else who's gone around the league the first time. You learn from what you see."

Berrios discusses rough start, mechanical adjustments

Jose Berrios took several minutes Saturday to apologize for leaving the stadium on Friday night without addressing the media following a tough start during which he allowed five runs on 10 hits in 5 1/3 innings in the series opener against the Tigers.

"Last night, I was not in a good frame of mind after the game, after everything that transpired after the game," Berrios said through team interpreter Elvis Martinez. "I just want to say that and be up front with you guys. That not like me to do. You know that as well.

"Like you guys know, I'm a competitor and we are battling to win the division. I felt last night that I'm not doing my job."

The right-hander has posted an 8.44 ERA in four August starts. Though he has gotten his fastball velocity back to its typical levels after making some adjustments, he is still trying to refine his command through additional mechanical work with pitching coach Wes Johnson and assistant pitching coach Jeremy Hefner.

"We are working on my front shoulder, trying to stay more closed," Berrios said. "Staying longer on my heel. I'm probably opening up, and I'm trying to stay closed."

Baldelli said that several of the indicators that the Twins look at with Berrios have indicated that his performance isn't too measurably different than in the past, when he was experiencing more success. As part of continuing to fix the execution issues, Baldelli also suggested that Berrios and the Twins' other starters could begin to get some extra rest.

"We’re still going to spend a lot of time on the objective part of what’s going on, and breaking down things mechanically and getting into all those questions, but I think those are finer-point discussions that Jose will have with the pitching coach, the bullpen coach and spend a lot of time on those things," Baldelli said.