No specific substance was identified. Privacy restrictions and the guidelines of Major League Baseball's Employee Assistance Program limit what team representatives are allowed to say regarding the problem.
According to a release from the team, no time frame has been determined for Spiezio's return. However, manager Tony La Russa said on Thursday afternoon that he "absolutely" expects Spiezio to play for the Cardinals again in 2007. Spiezio has not been suspended.
"This is something that we want to see happen, because he's having issues," La Russa said. "It's really important that he address them and take some positive steps to correct them. What we want more than anything else is to do whatever is best for him."
The Cardinals held a closed-door pregame meeting on Thursday prior to their game against the Padres. The clubhouse was not opened until 4:15 p.m. CT, more than half an hour after doors are customarily opened to reporters.
Spiezio last played on Sunday in the last game of the Cardinals' road trip in Washington. He was held out of Monday, Tuesday and Wednesday's games due to what the club simply called an unspecified illness. On Thursday, he was placed on the restricted list.
"I just wish him the best," said teammate Scott Rolen. "That's the thing. You want things to work out. I don't know what words to pick, exactly, and to say. You think about him, you care about him and you hope the best for him and his family."
"It's one of those things that kind of hits you out of the blue," said David Eckstein, who has played with Spiezio in St. Louis and Anaheim. "I just hope that everything is going to be well."
Matthew Leach is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.