"Obviously, Izzy's been struggling," general manager John Mozeliak said. "Last weekend he injured his hand. He's having a little trouble throwing right now. Is that the main reason for what happened? I don't know. But he does have a little infection on it."
Isringhausen will likely head to the Cardinals' Spring Training complex in Florida. Mozeliak said he expects Isringhausen to begin a throwing program in a week or so.
Following his Thursday performance, Isringhausen indicated that he knew that some sort of roster move was coming. He met George Paletta, the club's head physician, on Friday. According to Mozeliak, both Isringhausen's arm and his surgically repaired hip checked out with the doctor, but the hand was infected enough to allow a move.
In the absence of an injury, it's unclear what the Cardinals would have done.
"He's not effective right now," Mozeliak said. "So something's bothering him. And I think medically right now that's part of it. Are there other aspects that are affecting him as well? I'm sure there are. But the fact is, he's not effective out there. We have to put guys on the mound that can be effective."
The newest guy who will get that chance is Perez, who was drafted in 2006 and has rocketed through the Minor Leagues. Long ticketed as the club's closer of the future, it's unlikely that Perez will be relegated to mop-up duty. Mozeliak estimated that Perez might pitch in the seventh or eighth inning.
La Russa simply said that the rookie would get plenty of work. Perez, 22, was closing at Memphis. He had to be added to the 40-man roster as well as the 25-man, so Josh Kinney was moved from the 15-day disabled list to the 60-day in order to make room on the 40-man.
"If he's on the ready list that day, just watch the game," La Russa said. "Early, middle or late, whenever we need him."
Perez is the first player drafted by current vice president of scouting and player development Jeff Luhnow to make the Major Leagues. The University of Miami product believed he would be called up when Isringhausen first injured his hand, but at the last minute it was decided to keep Isringhausen active.
"I was just sitting in the locker room right before BP, and [Memphis manager Chris Maloney] came up to me and said, 'You're called up, this time for real,'" Perez said.
"He said they wanted to keep it kind of quiet, so don't tell anybody. So I was sitting there with all my friends, and I couldn't tell them."
Perez has refined his control this year, improving the one area that had been a problem for him earlier in his professional career. He still walks more batters than he or the club would prefer, but he's made progress. He attributes the improvement to a decision made in Spring Training, when he ditched pitching from the windup entirely. Perez now pitches exclusively from the stretch.
"Out of the windup sometimes I'd be really good and sometimes I'd be bad," he said. "You start the game out of the windup, and the first guy gets on -- you're back in the stretch. I think working out of the stretch has gotten my mechanics more consistent, and my release point, from the first batter."