"It was a swing," Glaus said. "It's been going on for a little bit. I got some treatment done on it Sunday, I got a little injection to try to get it to calm down, and it didn't really calm it down much."
Glaus started at third base and batted second for St. Louis, taking two at-bats before he was removed. He struck out swinging in his second at-bat, in the bottom of the third inning. He did not return to the field for the fourth.
"It doesn't bother him to throw, but once in a while when he makes a certain swing," said manager Tony La Russa. "I'm sure he'll be out x-number of days. We'll see."
Glaus sat out Sunday's game against Florida following a cortisone injection in the shoulder, and Monday's off-day allowed him extra rest from the shot. Still, he wasn't feeling right on Tuesday. Glaus expects to have an MRI exam on Wednesday.
"Not everything is a miracle," Glaus said. "We were hoping that it was going to be enough. Obviously, it wasn't, so now we'll do tests and see what those show, and based on that we'll have a plan of attack."
In his first season with the Cardinals, Glaus is batting .269 with a .371 on-base percentage and a .472 slugging percentage. He has 23 home runs, 89 RBIs and is likely a candidate for what would be his first Gold Glove Award.
Glaus was acquired from the Blue Jays in January in a 1-for-1 trade for Scott Rolen, who coincidentally has a long history of shoulder problems.
Matthew Leach is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.