The Cubs already are shorthanded with outfielder Milton Bradley sidelined because of a nagging groin injury.
Ramirez said he felt some discomfort after he doubled in the second inning to extend his hitting streak to seven games. However, he stayed in and struck out in the fourth. Ramirez was lifted defensively in the fifth.
In the Cardinals' eighth, Cubs reliever Carlos Marmol had to leave the game because of a strained left knee. He also was to be evaluated on Saturday.
Losing Ramirez leaves the Cubs with only Micah Hoffpauir as a backup infielder, and he can ony play first base.
"Right now, we're short," Ramirez said. "Bradley's out, and hopefully, I won't be out for a long time. We need some players. That's the bottom line. We have to get healthier."
Cubs general manager Jim Hendry was talking to the medical staff to determine whether to bring up someone from the Minor Leagues.
Infielder Bobby Scales was batting .370 for Triple-A Iowa after going 2-for-4 on Friday in a 7-5 win over Albuquerque, and Andres Blanco was hitting .327.
"We've got no bench," Cubs manager Lou Piniella said. "We've got an extra catcher [in Koyie Hill] and Hoffpauir and [Joey] Gathright. We're going to have to get somebody in here."
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.