Glaus felt discomfort starting in the middle of the game, and by the ninth it was decided he should come out. He showered and dressed after the game before heading to a hospital to be checked out.
"It feels better now than it did before," Glaus told reporters in the clubhouse postgame. "I couldn't stand up."
It was unclear what exactly was causing the pain.
"He felt discomfort in his stomach," manager Tony La Russa said. "We're not sure if it's something he ate or his appendix or something. But he had trouble moving."
Glaus said that he has not had his appendix removed. However, he noted that some treatment and rest had already caused the condition to feel better than it did at its worst, giving him some optimism.
"I'll go to the hospital right now and get it checked out," he said.
Brendan Ryan batted for Glaus, then Cesar Izturis moved to third base in the bottom of the inning.
Matthew Leach is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.