He suffered the injury while chasing a foul pop fly Saturday against the Chicago Cubs.
Several reports say Pujols -- who is batting .308 with a major league-leading 25 home runs, 65 RBI and a .751 slugging percentage -- likely will miss several weeks.
"This is the type of injury that you really need to re-evaluate 18 to 24 hours later," orthopedic consultant, Dr. George Paletta, told the Contra Costa Times.
On the team's Web site, head athletic trainer Barry Weinberg said he was not willing to guess how long Pujols would be sidelined.
It is the first time Pujols, who is the reigning National League MVP, has been on the disabled list in his 5 1/2-year major league career.
The Cardinals recalled first baseman/outfielder Chris Duncan from Triple-A Memphis.