KANSAS CITY -- Mark Grudzielanek was out of the Royals' lineup on Monday night because of recurring back soreness.
He was replaced at second base by Mike Aviles with Tony Pena Jr. moving into Aviles' shortstop position against the Colorado Rockies.
"Grud is sore in the lower back. I'm not sure if he's going to be available tomorrow or not. Hopefully he is," manager Trey Hillman said. "We'll see how his treatments go today but you won't see him on the field today."
Grudzielanek has been bothered by the back problem periodically since Spring Training. He has played in 58 of the Royals' 77 games and is batting .303.
He also sat out Sunday's game against the San Francisco Giants, a four-hour marathon win.
"It's not anything new," Hillman said. "We could have forced the issue yesterday and played him but actually it's a little bit more tender today."
Aviles also started at second base on Sunday after 15 straight starts at shortstop.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.