ST. LOUIS -- Having played in only four games since being acquired by the Reds, third baseman Scott Rolen wanted anything but to go on the disabled list already. But head injuries rarely can follow timetables, and Cincinnati decided there was no other choice.

Rolen went on the 15-day DL on Tuesday retroactive to Saturday, due to a concussion, while Chris Dickerson was activated and started in center field.

"This concussion thing is out of my realm of being able to grasp," Rolen said. "This isn't playing through a hamstring or playing through a shoulder. This is something I need to pay attention to and listen to some people. I need to do the right thing."

On Aug. 2 vs. the Rockies, Rolen was beaned by a Jason Marquis fastball and came out of the game. He missed two games, returned Wednesday and hit a homer in the first pitch he saw from the Cubs' Rich Harden.

But symptoms returned while the Reds were in San Francisco, and Rolen was sent back to Cincinnati on Saturday and diagnosed with a concussion. Testing has shown limited improvement.

Reds general manager Walt Jocketty said on Monday that he wanted to avoid placing Rolen on the DL, but the team apparently changed directions.

"He's not seeing much improvement from what he showed," Reds manager Dusty Baker said. "He got to a point where he's stuck with the headaches. He's kind of in that zone kind of thing. Walt was going to wait a day or two. But we're short on the bench. We're short in the bullpen."

Rolen met with Baker in the skipper's office for over 30 minutes. Rolen accepted the decision without complaint.

"Do I want to be on the DL? Of course not," Rolen said. "At the same time, I think it's the right thing. It's not something I want to battle with down the road.

"I thought it was OK, came back and tried to play. Then it went the wrong way. I played two games and did exercises, thought I was back and fine. I was kind of in la-la land in San Francisco and had lingering effects. This is the right thing, whether I like it or not."

Minutes prior to the July 31 Trade Deadline, Rolen and cash were acquired in a trade with the Blue Jays for third baseman Edwin Encarnacion and young pitchers Josh Roenicke and Zach Stewart. The move, the club said, was made to boost the club's chemistry this season and help bring improvement in 2010.

For now, that will have to wait. Rolen still gets headaches and was told the best way to get over a concussion was inactivity. He plans to heed the advice.

"They're not constant headaches," Rolen said. "There will be a minute where I feel great and think, 'You know what? This isn't here. I'm OK and everything is good. I will take some BP and get back out on the field.' Two hours later, I'm kind of squinting from the lights in the room with a headache."

Rolen was 2-for-14 (.143) with one homer and two RBIs in his four games with Cincinnati. He batted .320 in 88 games for Toronto before the trade.

By his estimate, Rolen has now had three concussions in his life. The 34-year-old believed another one came while he was a member of the Cardinals. As a kid, he also recalled being knocked out during a pole vaulting mishap at school.

"They all count," Rolen said.