"Before the game yesterday, it was tolerable," Duncan said on Tuesday. "And then after the game last night, when I woke up this morning, I couldn't move. It bothered me yesterday and then it got worse over night."
The Cardinals recalled outfielder Joe Mather from Triple-A Memphis to take Duncan's spot on the roster. Mather had been optioned following the Cards' game on July 17. The club was able to skirt the usual 10-day requirement for an optioned player to stay in the Minors because Mather is replacing an injured player.
The hope is that Duncan will need only the minimum 15 days to heal the condition. He already had a cortisone shot to help ease the pain.
"They're going to treat it, and they think in two weeks he'll be back," manager Tony La Russa said.
Duncan, who hit 22 home runs in 2006 and 21 in 2007, is batting .248 with a .346 on-base percentage and a .365 slugging percentage thus far in 2008. He'd actually been coming on somewhat recently, putting up a .297/.381/.405 line for July.
Now his progress will be halted due to injury.
"I couldn't sleep last night at all," Duncan said. "Then I woke up this morning and told them something was wrong there. It was pretty bad. I tried to sleep on the floor and the couch and nothing worked. It just got worse overnight, and this morning I couldn't move at all, really."
Matthew Leach is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.