DETROIT – Twins outfielder Wilkin Ramirez has been placed on the seven-day concussion disabled list — and he's not happy about it.

Ramirez, who suffered a sore jaw when he collided with teammate Josh Willingham in the sixth inning on Saturday while catching a fly ball, underwent testing Sunday at Comerica Park and showed some concussion symptoms.

Ramirez thinks that what got him on the disabled list was his answer to one of the questions. He was asked to name the months on the calendar, backward.

"I don't know them forwards," Ramirez said. "I don't know them in Spanish or any way."

There are other aspects to the exam, and it is unknown exactly what made the doctor — a Tigers doctor, by the way — conclude that Ramirez had concussion symptoms. But Ramirez said if it's because he couldn't recite the months of the year backward, then he wants to appeal the decision.

Ramirez planned to speak to Glen Perkins, the Twins' players' association representative, about his options. Perkins indicated in an e-mail that Ramirez missed on more than the calendar question and that teams are "always looking for a reason or reasons to err on the side of shutting the player down" if safety is an issue.

Ramirez said he still is sore after running into Willingham. "I ran into a rock," he said.

But he doesn't think he was hurt seriously.

"I feel the same [as Saturday]," he said. "I don't think it was right to go on the DL. I don't know. The doctor had me answer some questions and I answer them. Then [Sunday] he come out and ... I don't know. I'm very disappointed right now."

The Twins called up catcher-outfielder Chris Herrmann from Class AAA Rochester to replace Ramirez.

Plouffe progresses

Third baseman Trevor Plouffe took some swings in the batting cage on Sunday as he continues to make progress following a concussion suffered on Tuesday in Atlanta.

Manager Ron Gardenhire remains optimistic that Plouffe will be ready to be activated from the seven-day concussion disabled list when the team returns from its road trip.

Gibson backs it up

With Twins official Bill Smith in attendance, righthander Kyle Gibson offered his latest argument for being promoted from Class AAA Rochester by throwing eight shutout innings against Charlotte on Saturday.

Gibson gave up two hits and walked three while striking out seven. He improved to 4-5 with a 2.82 ERA while running his streak of scoreless innings to 18.

Gibson entered the game with a 3-1 record and 0.50 ERA in odd-numbered starts but a 0-4 record with a 9.00 ERA in even-numbered starts. So the Twins wanted to see him be more consistent, which doesn't sit well with a fan base ready to see the former first-round draft pick in a Twins uniform.

"It's understandable," assistant GM Rob Antony said. "We want to see him, too. We're just looking for a little bit of that [consistency]. This guy is going to be a big part of our rotation for years to come. We want to do things the right way, bring him up when the time is right, when he is going good and can succeed."

Harden update

The Twins plan to have a conversation this week with righthander Rich Harden, who continues to struggle through his recovery from shoulder surgery that knocked him out for all of 2012.

Harden experienced discomfort when trying to ramp up his throwing program a few week ago, so the Twins let him back off. Harden has been unable to get going since then.