The St. Louis Post-Dispatch reported the veteran third baseman aggravated a minor strain when he broke from the batter's box on a seventh-inning ground ball Tuesday night at Cincinnati. The injury diagnosis followed an examination Wednesday morning by Dr. George Paletta, the Cardinals' medical supervisor, the newspaper said.
"I think it's worse than the other day when he pulled it," Cardinals Manager Tony La Russa said.
The injury-plagued team is expected to place Pujols on the 15-day disabled list, where he will join right-hander Adam Wainwright (right finger sprain).
Outfielder Chris Duncan has been called up from Class AAA Memphis.
Right-hander Todd Wellmeyer has an elbow strain and right-fielder Rick Ankiel is playing following a five-game absence because of a right knee infection.
Right-hander, Joel Piniero (groin), will come off the DL Thursday to face the Reds.