CHICAGO -- Reds center fielder Ken Griffey Jr. exited in the fourth inning of Wednesday's game against the Cubs, complaining of stiffness in the back of his right knee.
The 36-year-old said he first had trouble with his knee while chasing fly balls during batting practice.
"I just hyperextended it a little in the outfield," Griffey said after the Reds' 4-1 loss to the Cubs at Wrigley Field. "It bothered me and just tightened up a little bit. This place is always tough on your knees with the surface."
Still able to start the game, Griffey was batting against Chicago's Greg Maddux in the top of the fourth when he appeared to take an awkward check swing attempt for strike three.
"It's when it started tightening up," he said.
Utility player Ryan Freel took over for Griffey in center field when Cincinnati's defense took the field for the bottom of the inning.
Griffey, who was 0-for-1 with a walk in two plate appearances, is batting .258 with two home runs and seven RBIs in eight games this season. In the first inning of Tuesday's 9-2 Reds win, he hit the 538th homer of his career.
The Reds said that Griffey is day-to-day. He will be evaluated again on Thursday.
"We'll see how he is when he gets here," Reds manager Jerry Narron said.
Griffey entered 2006 healthier than he had been in several seasons. He batted .524 (11-for-21) with three home runs and 10 RBIs in the World Baseball Classic and appeared poised to take that production into the regular season.
His homer on Tuesday doubled the long-ball total Griffey had the previous April. He didn't hit his first homer of 2005 until the final day of that month, but he was coming off a long rehabilitation from a radical right hamstring surgery.
Although he had arthroscopic surgery on his left knee last September, there were no health worries entering this season.
"Not having to worry about the hamstring, the ankle -- the biggest thing is just trying to get the [right] knee stronger day in and day out," said Griffey after Tuesday's game.
Mark Sheldon is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.